I bought some USB to TTL adapters on the cheap from China. The OS X driver was a little difficult to track down, but this thread cracked it: http://forum.arduino.cc/index.php?topic=261375.0:

Okay, drivers for mac do exist.
I always see www.wch-ic.com for the driver, but now I searched for "ch341ser_mac.zip" and found www.wch.cn 
The mac driver is here : http://www.wch.cn/downloads.php?name=pro&proid=178
The version is from wch.cn is a newer, you should try that one.