Here's another option that does it all-in-one if you want to end up with USB:
http://www.superdroidrobots.com/shop...asp?itemid=795
More info in this PDF document:
http://www.superdroidrobots.com/prod...TTL_Cables.pdf
Price is $34.00 plus $5.40 for USPS Priority Mail.
Just add the 9-pin ECU/radio connector and wire up the TXD, RXD, and Ground pins.
Power for the converter is provided by the PC's USB port, so no connection to the car's +12V (and no 12V to 5V converter) is needed.
Here's another one, in the UK:
http://apple.clickandbuild.com/cnb/s...R+and+variants
There are likely cheaper ones out there. I'll look some more when I have a chance.