Alright, looking through some ebay postings, I'm seeing a lot of units that look quite similar to yours but are being called 6-stage units. I am having trouble finding one with a permeate pump, too, but lots with the holding tank for pretty cheap.
This is the dominating one on ebay right now, seller has good ratings. Again, though, no permeate pump.
I might also note that my tap water is about 60ppm, so I'm not looking at a terrible starting place. As I understand it, that should increase the efficiency of a system for me, right?