The 2007 Chevy Trailblazer SS has the vette 6.0L 400HP LS2 motor. Stock they have a 13.5 second 1/4 mile @ 100 MPH. The upgrade capabilities under the hood are sick. Making one into a sleeper from hell wouldnt be hard at all, they already are. Straight from the factory GM has a plentiful line of optional accessories for them like multiple dvd players 1 flip down 2 head rest, onstar, sat radio and a bunch more all covered under the factory warrenty. Really they are quite the sh!t IMHO.
As for being a "sleeper", i expect few people would be able to understand how and why a chevy SUV just put the smack down on a so called sports car. They cost $10,000 less than a base model vette. If you added that kind of money worth of mods to a AWD model SS trailblazer a good race for you would be a corvette.
You cant get it for under 20K, but in a year you could find one used for that much.