There are many good wireless "G" cable/DSL routers with good web-based setups, often for quite reasonable prices. You can look at Linksys, D-Link, Netgear, Belkin, and so on, and find the features you want at the price you want to pay. The sticking point is the "AirPort Extreme compatible" part of your requirement. Apple's implementation of the "G" (recently standardized) standard seems to have problems with other vendors' equipment. It even has problems with Apple equipment!
If you're willing to wait for the "G" compatibility issues to shake themselves out, you can tell your computer to use the "802.11b compatible" mode of operation. It will work with "B" and "G" access points and routers, but only at "B" speeds-which are faster than just about anyone's home or small office broadband connection. When Apple releases the firmware upgrade that everybody agrees is the really final solution to compatibility issues, you can install that, then tell your computer to use "G" mode and do your file transfers much faster (your broadband will still be the same speed, since that's the limiting factor anyway).
Many people find that using a network cable is (not surprisingly) at least twice as fast as using 802.11g wireless for file transfers. Unless you MUST transfer lots of big files EVERY DAY, and you MUST do so FROM YOUR BEDROOM/PATIO/WHEREVER instead of near your router, you may find the "B" compatibility mode a lot less hassle in the end.