Actuelly sheer dumb luck! I do a search every so often when i'm bored and need something interesting to surf. jk. I keep an eye on carpet cleaning related stuff.. just search floor machines, encapsulation machines, floor scrubber, carpet cleaning. also try searching host.. host host machines or host cleaning.
I got my host reliant off of ebay for $125.00. Of course I actuelly bought two, both in parts in a box. spent an afternoon switching parts from one machine to the other to make one good one and now I have back up brushes, back up handle, and anothers set of belts. They is keeping yourself from bidding till about 10 hours out, but when you do, Add a good maximum above your bid so it auto bids for you, this can unmotivate a fellow bidder. And if you can keep an eye on it till the end, you have better chances of getting it.
There is a smaller rental version availabe for about $600.00 right now on Ebay and its a buy now plus free shipping. It is still cheaper then new but not sure how the newer rentals work.