I suggest you visit
Kelly Blue Book and
NADA I would also check
Autotrader.com to see what price people are selling there 350's. I did all three before trading my 350. Two dealers tried to screw me over on my trade. I didn't feel like going back and forth with the idiots so I got my keys and left. Sorry to use such harsh words, but "it is what it is". In Texas if you trade in a car then you don't pay taxes on the amount that was traded. For example if the brand new car is $25K and your trade in is $5K you pay tax on $20K instead of $25K. Hope this helps, also find out your payoff before going to the dealership.