Not sure if you've thought of this but if you have it backed up the
intake of the a/c system, then isn't that were the warm air goes in to get cooled? Wouldn't it be better to back it up to an output vent to get a cool airflow rather than a warm one?
these guys are UK based but they do ship internationally and seem to know what they are doing. I think they've got some cheaper solutions than $600 even with the forex.
http://www.water-cooling.com/