Reverse Osmosis

The cost for a quality unit with a 75gpd membrane is only going to be another $20 or so. While it doesn't necessarily sound like a better option than a unit with a 24 or 50 gpd membrane, do you really want to wait that much longer for water, especially in a pinch if something goes wrong? Besides, those ratings are under optimal temperatures and pressures, which can be rather hard to acheive in quite a few homes (even more this time of year). You'd be lucky to make 1 g/hr with a 24 gpd unit... even under ideal conditions, that's almost 8 hours just to make enough water for a 10% water change, or better yet, over an hour just to make 1 g to top off what evaporation has taken away. I wouldn't buy a unit with anything > 75 gpd membrane, as the rejection rate goes down once you get up to 100 gpd. What that means long term is that you'll spend more money on DI resin (versus using a 75 gpd membrane), as the DI will have more stuff to remove that the 100 gpd RO membrane let pass and the resin will be used up more quickly.

Take a look at some of these sites to get a better idea of what else is out there...
http://www.thefilterguys.biz/ (these guys are very nice and will answer any questions you have)
http://www.airwaterice.com/
http://www.buckeyefieldsupply.com/
http://www.spectrapure.com/

Money spent now on a good quality unit will save you money down the road. However, that doesn't mean you need to spend $250... there's plenty of good choices in the $150 range.