OS X comes with apache and php built in, so you have the basics for web serving already available, assuming you want to leave a computer connected to your wireless. There are several free solutions available (XAMPP or MAMP to name a couple) for a more complete solution. I'm pretty sure there are similar solutions available for Windows or Linux. Biggest downsides to this approach is the extra power required to keep a computer running in addition to your wireless and a bit more setup/maintenance effort.

A lot of this boils down to what service are you trying to provide. If all you want is a simple file server (file sharing), a wireless router that can share attached USB devices (like the airport extreme or the other one mentioned above) is probably good enough. Most wireless routers will let you setup a guest account and honor file permissions on attached devices. In OS X with an Airport Extreme it is very easy to setup a DropBox folder with write only permissions along with a read only information folder. I just tried this using my personal setup and then connected to it using my work laptop (Windows XP) with no problems at all.

Range will be an issue with any Wifi system. 802.11g can reach about 300' outdoors while 802.11n can maybe reach twice that. Indoor ranges are maybe half the outdoor range. Differences between individual routers are fairly minor since the driving factor will probably be your computers capabilities/limitations. A non-standard, standard called WDS does allow additional base stations to repeat a wireless network. Interoperability between brands of routers/access points is a problem. Several years ago I used an Airport Express to extend a Linksys wireless network for internet access and file sharing though other services didn't work through the Airport Express. Check with your neighbors and see what they have/try it out, you might find enough compatible routers to cover the area.

I think the simple approach would probably be best, though the engineer in me leans to the more complicated (i.e. fun) web solution.

-Eric