What a car really costs
The sticker price is only the start. Sales tax, title and registration, and dealer documentation fees are often rolled into the loan, so you pay interest on them too. In most states, a trade-in lowers the taxable price, which is worth hundreds of dollars.
Compare the total cost, not the payment. Dealers can hit any monthly payment by stretching the term to 72 or 84 months. That raises total interest and can leave you owing more than the car is worth for years.
A common rule of thumb
The 20/4/10 guideline says put 20% down, finance for no more than 4 years, and keep total car costs (payment, insurance, fuel) under 10% of gross income. Treat it as a starting point, not a rule.