These old Apple computers are worth up to $905,000—and you might have one sitting in your basement

In 2014, Bonhams put a rare Apple-1 computer up for auction in New York. Estimated to go for between $300,000 and $500,000, it ended up selling for a whopping $905,000.

Six years later, that's still the highest known price anyone has ever paid for a vintage Apple computer, according to the auction house. (In 2016, an Apple-1 prototype came close when it sold for $815,000.)

Launched in July 1976, the same year Apple was founded out of Steve Jobs' parents' garage, the Apple-1 was the company's first line of desktop computers. There were 200 models assembled by co-founder Steve Wozniak, and the one that sold for $905,000 was "one of the first batch of 50 machines built," Cassandra Hatton, a former director at Bonhams who oversaw the sale, tells CNBC Make It.

Corey Cohen, a computer historian who was recruited to examine the Apple-1, noted that it was in "superb overall condition" — with the motherboard having "no apparent modifications performed or removed." Most significantly, it was still working.

To the average person, an old Apple computer might not look all that exciting. In fact, an unknown woman reportedly dropped off an Apple-1 at a recycling center in 2015 after cleaning out her garage, apparently unaware of what she had, according to NBC Bay Area.

"As with historic books and manuscripts, the value of a vintage computer is determined by its rarity, historical importance and condition," explains Hatton, who is now a senior specialist and vice president at Sotheby's.

Here are some valuable vintage Apple products that might be gathering dust in your basement:

1. Apple-1

"It's very unlikely that one of these will sell for as much as the one Bonhams auctioned off in 2014," Lonnie Mimms, a vintage computer collector and founder of the Computer Museum of America in Roswell, Georgia, tells CNBC Make It. But due to its rarity, he estimates that most surviving models "can still go for anywhere between $175,000 and $475,000."

In 2013, Christie's auctioned off a Wozniak-signed Apple-1 for $387,750. And last year, it sold one that came with a built-in keyboard and the original instruction manuals for just over $470,000.

Whether you're looking to sell or buy, keep in mind that many aficionados have created Apple-1 replicas (or kits for building one), which are worth closer to $1,000, Jonathan Zufi, a hardware expert and author of "Iconic: A Photographic Tribute to Apple Innovation," tells CNBC Make It.

"Some sellers will tell you that their machines were signed by Jobs himself," he adds. "There are a lot of counterfeits out there, so be wary of such claims."

Although an Apple-1 could conceivably come with a Jobs-signed receipt, the Apple co-founder was not much involved with the actual building of the machines, and therefore was unlikely to have signed one, according to Dan Kottke, a computer engineer and one of Apple's first employees.

As Kottke, who tells CNBC Make It that he assembled many of the Apple-1 computers himself, recalls: "Steve was mostly in the kitchen making phone calls," while Wozniak, who designed the Apple-1, "oversaw assembly," but did not always build the devices.

2. Apple II

Introduced in 1977, the Apple II is best known for making Apple a driving force in a new industry. It was a commercial success and went on to sell between five and six million units by the time it was discontinued in 1993.

While an Apple II is worth dramatically less than its predecessor, some have sold for a few thousand dollars. In 2015, an Apple II in "fine condition" fetched $4,687 at a Nate D. Sanders auction. The computer base contained two original disk drives and the motherboard fully intact underneath, according to the Los Angeles-based auction house.

Incidentally, the very earliest Apple II machines were built without vents, making them prone to overheating, Zufi explains. The design flaw, which was quickly corrected, makes the very few non-vented machines worth even more — potentially up to $10,000, he says.

3. Apple Lisa

Introduced in 1983, the Lisa was a huge product flop. The early model's incredibly steep price tag of $9,995, unreliable floppy disk drives, slow read speeds and high error rates led to poor sales.

But due to its rarity, an original Lisa with its two double-sided 5.25-inch floppy disk drives can be quite valuable. In 2017, Auction Team Breker sold one for $50,300.

"[The Lisa] is significant in being the first computer to include many of the features we still use today; overlapping windows, drag-and-drop, pull-down menus and the recycle bin," a spokesperson for the auction house told The Daily Mail. Breker estimates that only 30 to 100 of these machines still exist today.

In 2018, another Lisa 1 sold for $31,250 at a Bonhams auction. It came with the original keyboard, mouse, Apple Profile Hard Drive, Apple Dot Matrix Printer and a collection of software and manuals.

Later Lisa models in excellent condition can go for anywhere between $2,000 and $4,000, while a non-working machine — or just its internal components — can still be worth a couple hundred dollars, says Mimms.

4. Macintosh 128K

The Macintosh 128K, which debuted in the legendary "1984" commercial that aired during Super Bowl XVII, was Apple's very first Macintosh computer. Priced at $2,500, it featured a nine-inch black-and-white screen, two serial ports and a 3.5-inch floppy disc slot.

Although Zufi has seen some sell for more than $2,500, he estimates that "an original 1984 Mac will generally go for anywhere between $1,500 and $2,000."

But even without the actual machine, the original accessories alone can make you several hundred dollars richer. In 2002, Wired reported that an empty, well-maintained Macintosh 128K box, which featured artwork by Picasso, sold for more than $500 on eBay.

Those who still have the boxy travel bag that came with the computer can fetch $100, at the very least, according to Adam Rosen, a collector and founder of The Vintage Mac Museum in Boston, Massachusetts.

5. Other vintage Apple products

Apple defines its "vintage" products as anything that has not "been manufactured for more than five and less than seven years ago." So don't be quick to toss out any old and unused Apple devices. Experts say that the older and rarer they are, the more money you're likely to get for them.

Even Macintosh models from the 1990s can be worth quite a bit. The Mac Color Classic II, for example, was released in 1993 in Canada, Asia and Europe, but never in the US — making it even harder to find today. Zufi bought one for himself for $2,000.

Depending on its condition and release date, early Apple mobile devices are also surprisingly valuable. "Some have gone for tens of thousands of dollars on eBay," says Zufi. "Sealed in their original boxes, they can be worth $5,000 or more."

In 2017, MarketWatch reported that a retired business owner named Bob Kraft "received an offer of $11,000 for an unopened 2007 iPhone that came in a factory gift box from Apple with a red ribbon." Kraft, whose original asking price was $15,000, turned it down. "It was tempting," he told MarketWatch. "But I'm not in a hurry to sell it."

First, check to see if it works; a running device will be worth much more. And if it doesn't work, don't try to fix it yourself or send it to a repair shop. Components should only be replaced with its original parts, and experts suggest you're better off leaving that decision to whoever ends up buying the device.

Next, research online (eBay is a good place to start) to see what prices they're selling or have been sold for. Keep in mind, however, that just because a seller has a high asking price, it doesn't mean that there are buyers willing to pay it.

The fewer listings there are of your item, the rarer, and hence more valuable, it probably is. "If you can't find one at all, that's the best case scenario," says Mimms. For truly valuable products, such as an Apple-1 or Lisa 1, he suggests contacting an auction house.

If all of this — not to mention the hours you'd spend digging through dusty belongings — sounds like more work than it's worth, you're not entirely wrong. "Most of us have older technology in our garage or basement, but very few have anything that's very valuable," says Hatton.

"However," she adds, "I've sold three Apple-1 computers now, and they all came from people who just had it in their basement for years." In other words, you never know.

Minda Zetlin is a freelance writer covering business, money, technology and collectibles. She is also the co-author of "The Geek Gap" and president of the American Society of Journalists and Authors. Follow her on Twitter @MindaZetlin.

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