with good research and patience buying parts you can probably do a reliable KAT set up for $2500-3000, which, as far as I know, is a bit cheaper than a SR20 swap, and should be a little bit faster than a basic bolt on SR... IA's full of idiots, I don't proclaim to know everything myself, so I'm gonna point you in the direction, nicoclub, freshalloy all have great info, much better than the info here.
PS: The mileage on the motor has NO direct link to how well an engine will take boost, it's based on the engine condition.