DIY RO Unit (inexpensive option?)

[MicroTankin]

Thanks for your opinions guys, I am not sure if I will try this or not. I know that you can get this system at Walmart (so it must not be discontinued). I have thought about a used RO system....

Mostly I would like to know where I can buy RO water for $1 dollar per 5 gallons......cause then I will just buy it with only one water change every 2 weeks to a month that will be a cheap option!! (sphelps??)

Thanks to globaldesigns for the info about Calgary water!

Obviously the most important thing for my small system is not introducing Phosphates via my water changes...this could be detrimental to my system....so I definitely need to use good water!