This is the one that I got off of ebay. It is a 6 stage ro/di and has been working great for the last 8 months. I also have a TDS meter to tell me when the filters need replacing. So far everything is good. This unit takes my tap water from about 260ppm to 7ppm total disolved solids.
http://cgi.ebay.com/ws/eBayISAPI.dll...323887031&rd=1
I couldn't find anything this affordable locally. HTH
- Chad