5 things you should never pay full price for

Certain comforts are worth the cost, even if they mean you spend a little extra. But, in other cases, you could save hundreds or thousands of dollars if you go with the secondhand version, negotiate the original price or simply shop at the right time, and it won't affect your experience.

Here are five things you should refuse to pay full price for.

The brand new car smell is tempting, but used models are often available for a fraction of the cost of new ones. Plus, the moment you drive a new car off the lot, its value depreciates by about 20 percent.

If you're set on buying new, make sure you're getting the best deal. For starters, when you buy matters, writes Yahoo tech columnist David Pogue in his 2016 book, "Pogue's Basics: Money." You'll typically get the best prices in September, he says, which is the start of the model year and when dealerships are eager to clear last year's inventory.

Always negotiate the price. Try the No. 1 trick of CNBC's Caroline Moss and don't mention money. She negotiated the price of a 2017 Honda Fit from $250 a month for 36 months to $179 a month.

College textbooks aren't cheap: Last year, students spent an average of $579 on 10 required class materials.

To trim your book bill, you have a few options: Rent or buy them second-hand using sites like Amazon's Book Rental, Chegg and Half.com; buy them in the off-season, before demand kicks in and prices increase; or consider free options like borrowing, sharing or downloading them.

Rising NYU senior Eric Hu, who is on track to pay his $200,000 tuition bill before graduation, saves hundreds of dollars a semester by cutting out this expense altogether. "I've found that most professors will send print-outs or PDFs," he tells CNBC Make It. "I don't even bother to buy any [books] off the list anymore, and that's the best advice I can give to incoming freshmen."

Chances are, you can negotiate the cost of registration or even the monthly membership fee. There's a lot of competition when it comes to gyms, so use that to your advantage when talking to the manager.

You may get an even better deal if you join in June, says Pogue: "That's when demand is lowest, as people head outdoors for physical activity."

Finally, look into your employee benefits. Companies often offer discounts at certain gyms or reimburse you for membership fees.

Memorial Day mattress sales are a real thing, Pogue says: "The entire industry blows out last year's models over Memorial Day, so watch for crazy sales in May."

If you miss out on this specific weekend, don't stress. More sales will come around over the weekends of July 4 and Labor Day.

As for furniture, you can save hundreds of dollars if you go with the like-new, second-hand version. Resale sites like Craigslist have everything from bed frames to dressers. Check out FleaPortal and Collectors.org for a list of different indoor and outdoor flea markets in the U.S.

You can also ask family and friends if they're looking to get rid of any furniture.

Prom dresses and wedding attire don't get much wear after the big event. If you're only going to wear a gown or tux one time, instead of buying, consider renting from sites like Rent the Runway or Bag Borrow or Steal. You can also check out consignment shops or thrift stores for gently used formal wear.

For brides-to-be on a budget, plan ahead: Even if the big day isn't until the spring or summer, start looking in November for a more affordable gown. "Nobody's buying wedding stuff in November and December," Pogue explains, "so that's when the bridal shops mark down their wares to make room for the new year's designs."

From splitting the check to DIY adventures, "Young Money" helps you navigate tricky financial situations.

Check out more in the series:

• A couples therapist says this is the best way to talk about money with your friends
• How I spent $1,230 on convenience in just two months
• Here's how much you could save by skipping these 6 convenience traps

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