11b probably about $10 these days if you can find one. Take look around in your neighbors trash - hehe
I found a load of books doing that in the industrial area when i was younger, evidently salvation army has no need for tech books as they where inserted into the trash bin...
I put an ad on Craigslist, but never got responses; and the guys on ebay charge what would cost me the same as an 802.11g lol