For 4-5 grand for a car, you'll be forced into a decent LT1, or a beat up LS1. Soo you'll just have to shop around and see what you can find.
I just barely installed a vortech supercharger, and I have longtubes, otherwise the motor is basically stock.... Im only running about 5 lbs of boost right now and would "guess" (havent dyno'd yet), that I'm about 340-350 HP at the wheels right now. Hopefully I can squeeze more out of it once I figure out how to tune it, and up the boost to 8-9#s or so.