Check out megasquirt.info. Its a do it yourself fuel injection kit using an open source computer and whatever mechanical parts you want to use. Its very customizable and supposedly can be adapted from everything to a lawnmower to a turbocharged engine. Apparently for the 258 people use a GM TBI and the whole project is supposed to be about $500. You can go for a version that simply controls fuel, or a version controlling fuel and spark with O2 feedback and all sorts of features.
I was hoping somebody on here could say exactly what parts they used, how much work it was, etc. It sounds like some people really tune the crap out of the thing and some guys get it working good enough without too much effort. I am seriously considering trying this out, but don't want it to consume me.