Trying to buy a great car?
I have owned a few of these cars, so let me help you. The Firebird Trans Am comes with a six speed manual transmission and an LT1 350 V8 (Corvette motor). Goes very fast and actually gets excellent mileage, right around 29mpg. I will warn you though. If you need full coverage insurance, the Trans Am is the most expensive and identical peformance to the Camaro. The Mercury cougar and Toyota celica are the same car. The cougar has a very weak value, while you'll typically pay almost twice as much for a celica. The V6 is ok, but will not keep up with a Trans Am or Mustang GT. The mustang GT might actually be you best bet. People are scared of buying V8's right now and even fewer people want the old body style mustang. You can find a good one for around $4500 while the camaro or firebird with similar V8's and trannys will fetch upwards of $8000. Also, the mustang is just as reliable, has comparable perfomance, cheaper insurance, but worse mpg. Mitsubishi Eclipse GT (V6) comes with everything the others do, except it has a five speed tranny. Excellent performance, won't outrun a chevy or ford V8, but, handles much better than the American muscle. You can cruise around 100 mph and still get 35 mpg. The eclipse is probably the best car you have on your list, but, is also the most expensive. They're all fun, fast cars. You just need to decide what the important factors are.
Gas mileage and handling = Eclipse GT (v6)
Off the line perfomance = Mustang, Firebird, and Camaro V8
Economy, no frills = Cougar, Celica and civic
Luxury, smooth ride = Accord