The cost of the new car is the bottom line cost to you. However, if you are claiming the sales tax as a deduction on Schedule A, you wouldn't include that with the cost of the car. The loan amount is money you are going to pay back so it is the cost of the car. Too bad it's not a gift.
Yes, for the old vehicle, put the value at the time you started using it for business. A fair estimate of the value is good. I always look at Kelley's Blue Book to get an approximate value now. They also have past year's value in their little books. I'm sure it's on the internet, everything else is.
