I've got a 75g tank and have grown tired of going to the LFS on a weekly basis to pick up 12g of RO water. I was looking in Fosters and basically the cheapest thing I saw was a setup for about 500, I've heard people saying you can get units for 100-150, is this true? What will a higher priced unit do besides produce more gallons of water per day? I only need about 12 a week.