I agree with plsoan. You can build a modest turbo'd engine on a budget for far less than 4K. I have been studying into this for some time and will begin the project in about a year. I already have a megasquirt (MS2,cable,relay) and all intake parts including alt, totalled $1100NZ (thats ~$550us). I will be looking for smaller numbers such as 150 at the flywheel, Mostly doing it for the learning process. but nice to give the car a little more punch. My brother had a turbo manifold built for his fiat. It cost $500NZ built by a prof, I dont know what steel its made of but its been going strong for 2 years now and I would expect it to last well past its being replaced in favor of the next crazy scheme.
I often bump into these guys at the local bmw wreckors who simply slapped a turbo on the side of their m10 318 e30 and away they went . (The doubt the thing makes great figures but its still running strong)
all in all. for 4K (8knz) you would end up with a very very powerful + reliable turbo engine.