I got a nice 5 stage RO-DI unit brand new on the bay for $96. 0 ppm money back guarantee. Also included a 6th stage carbon reactor to make drinking water as well(removes flavor). But I only have use for the first 5 stages, thats for the RO-DI tank water. Just do some shopping, these units are pretty cheap.
My only complaint is the manual was pretty lame, but most of these units all install identical...so I downloaded some manual's from a few other manufacturers. No big deal.