i love my GTO. the only thing i have done to it, is a tune/catback/intake and shifter--basically near stock. the car has just a bit of a rumble to it, but is nowhere near annoying at freeway cruising speed. at 80mph, i see 2k rpms, and 22-25mpg--smooth sailing. the car is fairly quick, and the interior comfort/quality is very "un-GM like". the ride is firm, but not harsh at all.
you can find '06's for under $20k i'm sure. if i were looking for a newer car to just drive as a daily, i'd stay away from anything older than 2004, as well as anything that's more than slightly modded. everyone here knows that the more you mod a car, the less 'daily driver' friendly it becomes, and it sounds like you're looking for a fun daily driver, but not something you will have to worry about reliability in. my GTO is a perfect daily driver as it sits right now. add a cam and longtubes, and i think you ruin things as far as CAREFREE daily driving and FACTORY RELIABILITY--which is what you need when you have a real job.