ebay has several auctions of Cabletron/Enterasys CSIBD-AA (Silver equivalent) starting at $20 with no reserve.
To find these on eBay, you need to search for Cabletron, Enterasys, RoamAbout etc. Then further look at the sellers online stores and their other items...not everything pops up in a straight search...
The following link is such an example:
http://cgi6.ebay.com/aw-cgi/eBayISAP...sort=3&rows=25
There are also Cabletron/Enterasys versions of the Lucent Range Extender antenna for as low as $19.95+shipping.