I found a RO
system on ebay for $101 (with shipping). A little later I saw the same one and the auction price seemed low so I bought another for only $65 and sold it to my brother. So, if you are a lucky, patient bidder they are not too expensive.
Chemicals are not that expensive, but bottled water is. The best reason I can see for bottled water is to lower the hardness. This is why I bought mine. Now looking back, I I think I should have found fish to match my water instead.
water is very pure - too pure for fish and plants. You will have to either add minerals back using store bought products or mix with tap water. But you still need dechlor for the tap water.
system (Aqua-safe) I got on ebay has 6 stages. The first 3 are activated carbon - then the RO
- then another filter (I don't know what this one does) and the a DI
. The carbon gets out chlorine and other chemicals (and maybe ammonia). So I run half the water through all 6 stages, and the other half through only the carbon filters. This gets rid of chlorine but leaves some minerals. Then all of it goes straight into the aquarium. I've never heard of anyone else using this method, but it is working very well for me.
Softer water leaves less crusties on my tank, and I don't use any chemicals at all except plant fertilizers. Both are nice but I still would suggest finding fish to match your water instead of water to match your fish - RO
systems can be kind of a pain.