Posted by someone who probably has never had to pay electric bills ... LOLI would recommend an AC for an 8 x 6. A lot a lot easier.
When looking at any of the systems that use water, get an estimated usage. I suspect that it will be much higher than your RO can handle ...Was thinking of buying either the evaporative cooler or a misting system involving a resovir of RO water that is pumped to the misting hoses and have a fan to periodically circulate the air. Both are probably the same price but which would be better to cool down the GH.