They are not as expensive as you think. I got one off e-bay for real cheap to. i purchased a portable one so that I can put it under the sink when not in use. If you absolutley want to start using Ro
water for the tank and don't want to purchase a RO
unit yet, just go your local health food store. They should have one of those machines to fill jugs of water (5gallon). That should only cost you a couple of bucks. Since you are starting a rather small tank, I would get the 5gallon jug and a 1 gallon. The reason being that the 5 gallon will make it easier (less trips to the store) to fill the tank. The smaller will allow you to purchase a small amount to allow you to do your water changes. Unless you have one of those stands that you can put the jug into and drink the remaining water after you use what you need for the water changes.