If you are going to be taking business expenses for your vehicle, TurboTax asks how much you paid for the vehicle to determine your cost "basis".
Even if you took out a loan for the purchase, the way its reflected or considered is as a payment for entire amount of the vehicle at the time of purchase. If you received value for a trade-in when you purchased the vehicle, the value of that trade-in is also added to any cash paid or any loans taken out for the purchase.
For example:
If you buy a new car for $30,000, and you're given $5,000 for your trade-in, then your "cash or loan amount" is $25,000. It's the amount you have to pay after subtracting the value of your trade-in.
