Quick question, Does anyone have an estimate of how much it cost to filter per gallon?? My system is less than 50g total. I evaporate around 1/4-1/2 gallon a day. I have been using bottled distilled water since day one. I have been paying .99 per gallon at wall-mart, so it cost me between .25-.50 per day in water. Just trying to figure out if it would be cost effective to buy an ro/di unit.