Interesting stuff. I was thinking more along the lines of what could I find in a junkyard, but the advertisers don't like that, I suppose.

Syclone turbo or any number of diesel turbos could do the job - like a holset hx40.

Use twin turbos and there's all sorts of possibilities. I'd toyed with using 2 WRX turbos for my 4.2 (Mitsu TD04-13T). You can score these turbos for $150 each and they will push 22 psi in the midrange everyday and twice on Sunday. The fab work involved with a twin setup scared me off though.