Price Research: Our research indicates that OBDII OBD2 V1.5 Bluetooth Auto Diagnostic Interface Scanner (ELM327) is $8 lower (40% savings) than the next best available price from a reputable merchant with prices ranging from $20 to $25. - Discombobulated
this is the cheapest I found so far.
with the suggestions of others I thought id post a few apps out there you can utilize this device.
Torque Pro (paid) / Lite (free)
OBD Elm 327 (Free)
Engine Link for iOS (you need jailbreak) https://itunes.apple.co
You cannot use these cheap adapters with iOS unless you jailbreak. Apple's walled garden means you need to pay them for an authentication chip to connect via bluetooth to an idevice. $12 for the whole device is not enough to pay this tax.