Used cars are worth what someone will pay for it....
You might find someone to give you 10,000.00 for it, but right now average to good 2003s are running 5000-6000.00....
if you continue to maintain it, you could get 300,000 miles from it, and not need to buy another car for ten years or so...
If you would do so, and then put away the amount of money, you would have paid each month in car payments, you would have enough money to pay cash for the next car......