"If you own the new LEGO® Mindstorms® NXT v2 Kit (Set 8547), this Unofficial NXT Retrograde kit contains just about everything you need to build robots designed for the NXT v1 kit (Set 8527). You get 180 lego elements, including an NXT sound sensor"
Even the tricky sound sensor! Priced at $80 US, I'd say this is a fair deal. The website says it is in limited stock, so you might want to grab it if you need it while you can!
If anyone purchases from here, let us know how it goes!