The usb adapter cables will charge only, not sync, and the 30-pin adapter cables are more expensive than the cables themselves.
When I found myself in this position, I bought a few cables with Best Buy reward zone certificates which drastically lowered the price, and I bought a few from Other World Computing who was selling genuine cables un-boxed for a good price.
You can also buy licensed cables from Amazon, Monoprice, etc, but I found the savings wasn't that great and the connectors were bigger than the genuine cables.