Honestly, these days, I'm not totally sure it's worth doing. If you can get a on3 kit for $1,500, even if you have to fix/fab a few things. Putting an M112 or M122 on involves a lot of fabrication - making a diy turbo kit is a walk in the park by comparison. While it's true I spent less than a grand getting the thing on there, the blower was given to me, I happened to have a lot of stuff lying around (like most of the pieces for the tensioner assembly), and I wasn't afraid to hack up alot of parts to fit - valve covers, motor mounts, even poly locks. Ultimately, a turbo will have more power potential. But nothing beats driving a positive displacement car on the street.
If you want to give it a shot, it can certainly be fun and very rewarding. As far as I know, mine is the only such project that's actually seen track time and put up halfway decent results. Most people give up and go down a path of less resistance.
My $.02.