They aren't invincible....but they do run good. First and foremost I'm only gonna speak of 6spd cars, since the un-stalled auto's aren't all that great from what I have seen. I don't think it'd be THAT hard to beat one with a cheap setup, but theres no such thing as a 'budget' efi build imo. Convert to carb, work a set of heads, with exhaust and gears and you should be pretty close in a 5spd FOX. An sn95 will need more work.
I've seen the ls1's run all over the board too. I've beaten them through the beginning of 3rd (its already stupid, but im not gonna kill anyone on the street) in my LT1 6spd car, which uncorked they seem to go high 13s @ 102-3 on street-tires. An uncorked LS1 with a TUNE! (this is soooooooo crucial) will go LOW 12s as they will dyno @ 360rwhp with a lid/headers etc./tune combo.
It really depends on what #'s your h/c/i gets you and what mods you have before you go KBing a car. It's sad but it's just how it is. There is no replacement for displacement.
Go work on the LS1 though, its much more of a PITA. I fret working on my LT1 car like no other.
My only latest gripe with LS1 cars is piston slap. Read up on it and see how sicking it is to see how many are affected when GM got away from selective production. My brothers Z has it, there's cars on the board with 17,000 that have it. They still run like raped apes...but I find the noise rather un-nerving.