I don't have a $4000 budget, or i would. i don't know the first thing about turbos, except i love the sound they make.
A turbo won't cost $4000. Do a little snooping around, I'm sure you could find a used turbo kit for cheap. The Z3 kit on ZZP isn't too bad of a price either. With all the money I spent going supercharged, I wish I just went turbo been done with it.