I sourced most of the parts myself, except for the wiring harness/control module. I bought mine from epowersteering.com
If you want to save a few bucks, 2002-2007 Saturn Vue and 2005-06 Chevy Equinox units is what most use. Mine is from a 2003 Saturn. I bought an entire steering column from a junkyard for $150, plus the Basic controller from EPS for $85. I got the controller that comes with the potentiometer to adjust how much assist the unit gives. The shaft on the unit is a weird size, 16.5 mm so it takes special u-joints, not your standard 5/8 or 3/4 steering shaft size. epowersteering.com has the joints with the correct 16.5 mm size if you go that route.
I have had mine installed for over 2 years, with a Saco standard rack. I have had zero issues with it in both race and play modes. I'm running a full bodied, pan class 5 with 33" tires. Has not had an issue and once I converted it, I couldn't believe I hadn't done it sooner. The adjust-ability with the knob is awesome too as I occasionally drive my car on the street and don't need full assist, but can easily turn it up drive the car with one hand and not be fatigued at the end of a race.
I just installed the epowersteering.com unit on my car. I haven't had much seat time yet but so far it is awesome. Some people talk about a loss of feel but I do not find it to be an issue. You can save some $ if you are close enough to pick up the unit from the epowersteering.com guy in Ramona Ca.