I'm looking for a cheap elm327 and that looks like it's gonna be a USB one like this. Even though its usb, does it have a serial output that I can interface easily with the arduino? Say if I cut off the end of the cord, will there be wires that can interface easily with it? Thanks.
It is unlikely that you can use the "USB" signals although I am not positive but, if you can take the box apart and get to the ELM chip rx, tx then you might be able to do something. I have found information in the past that suggested that the ELM chip is based on a PIC chip.
Look at this - http://www.obdsol.com/stn1110/
It's fully ELM compatible and has TTL-level serial for interfacing to an Arduino/ATMega. They also give samples.
I have used these and it's as simple as it gets to interface with the Arduino.