I have used megasquirt for a few years now. Highly recommend.
Of course DIY means that the tune is only as good as the tuner... strongly recommend getting a good wideband o2 sensor as it make s a world of difference to tuning.
MS takes time to install and can be upgraded in millions of ways if you have a soldering iron and patience but do not enter into the MS realm unless you're prepared to spend hours researching and reading how it works and how to modify it for your application
. Even if you get a pre-built unit you will most likely have to do some soldering on the ignition circuit to determine the best signal method for you.

However, the aussie dollar has never been better against the greenbush...

-pete