This is the cheapest I can find for these. Much neater option than the play and charge cable etc.
Recharge in a flash and kiss disposable batteries goodbye with the Xbox 360 Quick Charge Kit. Quickly recharge up to two battery packs at the same time. Your Xbox 360 Wireless Controller needs a new battery? Swap in a fresh pack from the Quick Charge Kit. One rechargeable battery pack is included in the Quick Charge Kit. Additional packs are sold separately.