Oren,
We do this kind of setup for amusement parks where the games and attractions need to communicate with a central bank server. We've found that it matters a _LOT_ what hardware you use. There are a lot of units out there that just won't cooperate with this kind of setup.
We use a very expensive (~$600) Cisco central access point with a couple of ~$100 antennas, and Lynksys WET200 routers as wireless-to-wired remotes. Trying to do it with cheap hardware, we ended up spending a lot of money on hardware we couldn't use.
Not all of the sites have used the Cisco though, I'll check with our field engineer tomorrow on what else has been tried. We require wired-equivalent reliability, which it doesn't seem you would need, so a less expensive and not quite as reliable system might work for you.