I just picked up a cheap POS Actron (CP9125) reader off the shelf at Pep Boys to diagnose a non-firing cylinder problem on the MINI. I think it was about $40.
But there was that slick one Clyde pointed out a few months ago that I found intriguing... about $100.
http://www.appletell.com/apple/comme...-for-mac-os-x/
http://forums.carmudgeons.com/showthread.php?t=31173