PLX Kiwi Wifi + iMFD: $150
($200 at http://www.plxkiwi.com/kiwiwifi/hardware.html)
I've used the Kiwi Wifi to datalog and clear/diagnose check engine lights on other cars. I have not used the iMFD functionality, since that is generally used with the below item.

PLX Air-Fuel Ratio Sensor Module w/ Bosch Wideband O2 Sensor (new): $150
($210 at http://www.plxdevices.com/wideband.html)

or buy the complete set of PLX for $275 ($410 from PLX)
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all prices include shipping (to continental U.S.) and paypal fees

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Don't let a tune cost you your engine; wouldn't you like to know how it's affecting your car?