i recently did some ro/di researching
& did a bit of price comparison
what i ended up w/ was this
http://www.aquariumwaterfilters.com/RODI/Barracuda.html

got the 50 gal/day unit
which realistically only generates a little over a gallon/hour

also got the 4gal storage tank
they'll sale it separately from the kitchen kit if you ask

you can buy the 40 gal tank, but it is not pressurized
you could probably do the same thing w/ a trash can