Wow, wonder if I'll get one as well? Anyway, the size of the tank really doesn't matter IMO when it comes to a RO/DI unit. I have a 100gpd unit so this means I can fill a 5g bucket in a little over an hour. A 50gpd unit would take you about 2 1/2 hours to fill a 5g bucket...
Some here have been finding RO units on the auction site.
I have a Typhoon III (RO/DI Unit) and love it. You should at least take at look at the Typhoon III before you buy any other unit just to compare. Some things to look for are, auto shutoff valve, DI Unit!!!!, Backflush valve, replacement filters (the typhoon is a standard size which means other filters are interchangeable), TDS meter, Pressure gage and the gpd the unit is rated for.
Good Luck,