Do any USB 3.0 to Gigabit Ethernet adapter work with OS X?
StarTech makes the USB31000S, which is a USB 3.0 to Gigabit Ethernet adapter with support for VLANs, jumbo frames and checksum offloading. List price is about USD 55.

These are based on the ASIX AX88179 chip, which has drivers for OS X 10.6 - 10.8 available (bottom of previous link). Any other product using this chip would also work.