Wow.. That one on ebay is almost exactly the same as one I just built out of PVC and parts from home depot.. $10 for enough parts to build 3-4 of em. (w/o figuring in the N Connector)

Design here:
http://www.netscum.com/~clapp/wireless.html

Gotta love refridgerator coil, some washers, and some 1/8" threaded rod.. All you need is a dremel and some decent calipers.