Turbos are not that expensive, and the power gains can be substantial once tuned.
My friend has a basicly stock 440 (although studded and beefed up) with twin turbos and is making over 700hp.
Mostly it's time invested to get all the plumbing fabricated, and getting everything tuned.
The problem is that people modding their daily drivers want something they can bolt on and go, and not tie up their daily car. Unfortunately with the advent of EFI and OBDII, as well as EPA rules for emmissions have killed the American rodder. Hotrodding cars today is limited and the rodding spirit to "do it yourself" just isn't there anymore.