Have you tried Mikrotik Routerboard? I know they are cheap and wireless oriented too (but they use proprietary router sw) but I've never had the opportunity to try one.
http://www.mikrotik.com/http://routerboard.com/
I haven't personally used Mikrotik products, but I know a few people who have and they really like them. It's on my list of things to buy and try out when I have time & money
