This'll sound stupid to anyone who doesn't like American V8 cars, but if you want something with pep that's somewhat modern, doesn't gulp fuel like crazy and won't break the bank, I'd argue the Corvette C5 might be your best bet.

Bone stock they make like 350hp, higher mileage ones are less than $10,000 (and even good low-mileage examples aren't above $20k) and they're known for being pretty damn reliable. Fuel economy isn't great, mind you (it's a V8, whadaya want?) but for a V8 it's impressive; you could feasibly achieve high teens or low 20s out of the LS1s so long as you aren't fondling the gas all the time.