Almost always, a car will end up costing you more than the sticker price — and not anticipating the true cost is "the absolute biggest mistake first-time buyers make," says former car salesman Matt Jones, who is now the senior manager of insights at Edmunds, a car-review site.
"People get fixated on their car payment," Jones tells CNBC Make It, and forget to factor in all of the expenses that come with actually owning a vehicle, like gas, maintenance and repairs.
There's also insurance, he adds, which can be higher for first-time buyers, as they're typically on the younger side and don't have as much driving experience.
"Take a look at your car deal with a 360-degree view," says Jones. That means using sites like fueleconomy.gov to research fuel prices in your area and the gas mileage of the car you're interested in buying. Next, get an auto insurance quote using sites like State Farm or Geico.
Other hidden costs that come with buying a car include: depreciation, interest on financing, taxes and fees, parking and maintenance, like oil changes and replacing brakes and tires. You can use Edmunds' "true cost to own" tool to better estimate these expenses.
Finally, if you're buying from a dealership, chances are you'll be encouraged to buy a handful of add-ons before wrapping up the sale.
"The selling definitely doesn't stop after you agree on the price," former car salesman David Weliver tells CNBC Make It. Most likely, the salesperson will "try to sell a bunch of little things to you, from warranties to paint protection."
"They present you with so many different things you can buy that most people think, 'I should buy something,'" continues Weliver, who now runs personal finance website Money Under 30. "You have to be prepared for that. If there's anything extra you want, know that going in — and also know that it's fine to say 'no' to all of it."
Don't miss: Jay Leno's No. 1 rule for first-time car buyers
Like this story? Subscribe to CNBC Make It on YouTube!