I'd save some cash and buy a third party wirless router, and here's why. The most compelling reason to get a third party wireless router is that you can get one with external antennas. That's right, plural. Two antennas are important because they help the router receive weaker signals, and you can adjust the way they're oriented so that they perform even better. And you can get these things for half-or LESS-of the cost of an Apple wireless device.
Sure, you won't get Apple's cool styling, nor will you be able to configure your purchase with the Admin Utility, but then Apple is the only company I know of that doesn't use a browser-based interface to configure their network equipment anyway.
Unless you simply MUST go for streaming your iTunes throughout the house (and still have some issues about where you listen to the music), go with a third party box. I personally like Linksys (don't believe the propaganda around that Linksys doesn't work with Macs-it's bunk), but a lot of people say glowing things about Netgear, D-Link, and others as well. Asanté gets high marks, but they charge you extra for being Asanté (kind of like Apple). Shop around and get the best deal you can; you'll be surprised at how little you need to pay.