IIRC, the software is ~$80, and then you need the correct definition file ($EE, I think), which is another $20.
As for the harness, I too wonder why folks pay the ridiculous $$$ for the aftermarket harnesses......
Don't forget to download freescan and get a connector from Andrew (links on Tunercat's site).
Also, the OBDI DLC connector can be grabbed from any GM OBDI car at the JY. I got mine from a cavalier.
Tim
{edit}Tuner software is $69.95 and the definition file is $19.95