All the wireless options are a bit pricey. However, wired options are quite affordable-and can be plugged into any wired port of any wireless router. My own network drive is like that (A CoolMax CN550).
Of course you have to keep in mind that a wireless network connection is going to be really slow, even compared to a wired 100Base T connection (which will seem very slow as compared to a USB or firewire connection).