I'm betting that the kits that come from some guy putting together "turbo kits" on Ebay will still require a lot of fabrication, tuning, and additional parts to get running. One kit I saw included a lot of thin-wall tubing that looked like the stuff from cold air intakes, combined with silicone joining sleeves and a turbo from a bulldozer or something. It might be just me, but I don't think something like that would last a long time, or even work right from the beginning. I think there's a reason the established turbo and SC kits are so expensive- they've been refined after many installs, and they're pretty much guaranteed to work right out of the box.
If you weld or know someone who does, it shouldn't be too tough to fab your own setup. You'll have to do all the math on the turbo and plumbing, and get a tune before driving the car, but I've seen people get some reliable setups that way. Hot Rod magazine just had a writeup on a guy that made his own turbo setup out of spare parts- the oil lines were household plumbing fittings- and it worked just fine!