You could use a water deionizer like the one jack warley sells they work good for smaller set ups the filters only work at 100 % efficency for the first 125 gals Than they slowly drop off and need cartrige replacement I just so happen to have extra brandnew ones and extra filter cartriges. please do some snooping around and let me know if your interested I'll sellsome cheap just comeup with an offer.
from 12.oo to 17.oo retail you can use it after 125 but it wont be 100% pure they change color as they get dirty so its easy to tell when its time for a new one . The amount of use you get out of one also depends on how many disolved soilides and other crap is in the water are in the water. Like it will last longer on city water than well water depends on the source.
Looks like an excellent choice. Which one are you getting? If you're looking to get new though, try www.airwaterice.com. Otherwise, don't forget the 6% rebate for DFS.
a lot of it depends on the design and type of filter. Example, my carbon block and chlorine carbon blocks are recommended to be changed every 6000 gallons at my current water conditions. i tend to change my sediment filter every 10,000 gallons per its rating. water plays a big role, i live on city water, so i try to remove more sediments, chemicals then say well water.