Hi, you could have a look at Tormach Pathpilot and there is info on you tube. http://pathpilot-on-nontormach.wikia.com/wiki/Main_Page. They were Mach people until recently. The benefit of this route appears to be the DIY following and a company in the US who want it to work.
I am looking (still!) at doing a conversion and i think moving away from computers is the best route and it appears that single box controllers are the way to go and how much you spend will depend on the value you put on reliability and back up.