Food for thought, depending on your incoming TDS, Sediment/Carbon/DI is an option. I crinched the numbers last Friday on usage based on an incoming TDS of 43ppm. A square foot of mixed bed DI resin would run about 8,500 gallons of water. Came out to 4.9 cents a gallon as I recall.
Now, someone running the Dual Membrane RODI needs to cross reference to see what is more economical. For me, living in the high desert, water is expensive so cutting down on backwash (wastewater) is very important.
Oh, and Buckeye Hydro is who Bulk Reef Supply gets their parts from in case anyone wanted to cut out the middle man or customize their water filtration setup.