if u had searched, the answer is there http://www.badmintoncentral.com/forums/showthread.php?t=31083&highlight=rsl+diamond
The RSL Diamond Limited Edition. But that's not really playable nor readily available. The most expensive playable racket would be the SOTX Woven 16 at ~$300USD. Why? It's Woven UHMG in both the frame and shaft for super durability. It's warrantied up to 35lbs.