popatim :
05+ grand prix gt or gtp should be around 4k with a real reliable 3800 engine that should get 32+mpg highway. The gtp will be supercharged and still get the same mileage. Theres aslo a v8 gxp version but only gets 25-ish.
Until the head gasket goes out or the transmission fails in a big bad way. Buddy of mine had a GTP with the supercharger and no mods. His head gasket went at about 70K miles. At 100K the transmission went. It's because GM went cheap with those supercharged motors and using regular parts, not higher quality parts for the higher engine output. Same problem exists on just about all of the 3.8L Series III (I think) supercharged engines. The Monte Carlo SS, the GTP, I think some Buick's had that same set up.
For $4G's you won't find much, hate to say. I'm in the same boat as you, and I've had a LOT of cars (never any wrecks, just get bored with them and move on.) I've had the following:
1. 1991 Ford Festiva (Who needs a hybrid to get 40+ MPG? I got almost 50 MPG in that thing, and since the engine was MAZDA design, and so were the other mechanical parts, it lasted forever. Too bad no acceleration. I had a rosary next to me when I got on the freeway though cause I was praying to live! And I'm NOT catholic!)
2. 1993 (I think) Dodge Dynasty. (Called it the Die NASTY. Had it all of 3 weeks and got rid of it. Lost $1000 on that deal.)
3. 1992 Ford Thunderbird (awful 3.8L V6 engine, blew it's head gasket)
4. 1988 Mazda RX-7 (Second Gen, Nice car, but needed work every other week)
5. 1998 Saturn SL (base model, 4 door, Only option it had was A/C)
6. 1993 Honda Civic DX Hatchback (All I can say is "Thank God for Alarms!")
7. 1989 Nissan 240SX XE Model (Think Silvia, with pop-ups. Damn truck motor under the hood was a SOHC, but had good torque!)
8. 1993.5 Infinity G20 (Nice car, had the SR20 low port, very fun to drive, but very stiff factory suspension. I called it the "tooth chipper" and damn expensive to fix!)
9. 1998 Saturn SC2 (Great car, but I felt like it was too feminine for me. Good power though, and solid. Until the tranny went out after I sold it.)
10. 1998 Chevrolet Cavalier LS 4 Door. (Still running, @ 214K miles. Just gave it to a family member.)
So I've known GM and Mazda to be the more reliable (at least in my experience) and often the cheaper of the bunch. If you live in an area where they salt the roads in winter, get a Saturn. Sealed under body and plastic doesn't rust. Also, dead simple (and really easy to drive stick shifts.)
Also, FWIW most of the Honda's and some Nissan/Infinity's I've come across (and owned) had had a chronic problem with bad axle's (namely the CV boot.) The dust cover almost always rips and you get grease everywhere and dust gets in, contaminating things and it's all bad times from there. If you do look at them, pop under the car with a flashlight and give it a look-see. If it's torn, try to get about $300-$500 off the asking price to fix it. It's a PITA.