I purchased one from a local water company, it does 150gpd, be aware that the gpd is misleading, that is assuming your water is a certain temp and pressure, which in our area the water is like 56 degrees and the pressure is like 40psi or something, I had a permeate pump which really helps. I think all installed it was $400 w/ an extra tank.
from airwaterince.com
"
Permeate Pump: What if you want to save water AND improve performance? Then you want a Permeate Pump. The permeate pump increases the pressure of the water stored in the pressure tank. It also reduces the backpressure caused by the storage tank. With little or no back pressure, the membrane becomes very efficient. In fact, you can save up to 80% of the waste caused by a normal system. Better water, more water, and far less waste."