pick up a nova, theres tons of aftermarket and you can get them relatively cheap compared to the over done chevelle or Camaro. You should have far less problems with an older car than a new one because at least on a chev its 3 wires and youre up and running. Fuel mileage isn't as bad as a lot of people would like you to believe.
If you do look at mustangs pick up something 1970 and older, the 71-73 mustangs are ugly as sin and were notorious for rotting out. Your best value in a mustang would probably be a 65 since the 67-70 mustangs are the most sought after.
Of course theres other nice older cars/trucks (ford galaxy 500, C10, pretty much any and all Plymouth's but theyre highly sought after)
2009 Ford Escape Limited - 3.0L, 6 speed auto, 4x4, 25/33 city/hwy imp mpg.
2017 F150 XLT-XTR - 5.0L, 4x4, 3.55's, E-locker, xtr chrome package, fx4 off-road package.
20/25 imp mpg