If you've got a laptop, you're well off with a usb tool like this one on Amazon at $29, free shipping. You can find it on ebay cheaper or in a bluetooth model for Android/Windows smartphones. Be advised that bluetooth models don't work with the iPhone or iPod touch due to Apple's choices.
If you want a cheap scanner that works without a PC and shows you real live data without going used on Craigslist, I recommend the C•Reader V, currently $67 on Amazon. It's as full featured as the popular $200-ish models from Equus/Actron, less the pre-96 and ABS coverage of some of the specialty models. The manufacturer has been good about supporting users with updates and the like, and all at no cost.