Car trade in advice needed.

I currently own a 2008 mercury milan base i4, and i love the car but me and my fiance have decided on getting something different since we already have a family car. Weve been looking into some old muscle specifically a 1973 javelin amx. The thing is we want to trade my car in, but i still currently owe 7500. I ship out for boot camp feb so we were wanting to do this or find a cheap car so that i wouldnt have any monthly payments. Any ideas?