If you want go all out DIY, here's a link for plans to build air driven skimmers from scratch. First link on the site provides the info. The "Skimmer design 101" link is a good read as well.
I have a DIY cc air driven skimmer that came with the used system I purchased. Quite happy with it, works well, quiet, very low power consumption.
http://www.hawkfish.org/snailman/snailmandiy.htm