Yes there are a few out, I saw the Nyko one at Circuit City today actually. If you go to the hardware section and do a search there is a thread with all of them and pictures. It was by surfinrach. I'm too lazy to find it for you but it's a good thread.
One of my friend's just bought rechargable batteries and a charger, He said it was like 30 bucks, so I think pricewise it's about the same. I have a bunch of batteries that I already got so I'll probably wait till they're through and then pick up a charger.