You just want to make sure it matches up to the one you are pulling out to make it a simple swap.
Are you involved in any local car clubs or such? Know where car guys may hang out on the weekends? I'm not lying when I say lots of us have C4s sitting around. I have one right now just taking up space I would be glad to just give away (Chicago area). $150 seems a bit high to me. Offer up a lesser number if you think it really is an operable trans. He'll probably take it.
I'm not really hooked up with any clubs, but there are plenty of people here w/in 10 miles of me, none of whom are volunteering their services or wares.

He's actually asking $200...if it were a guitar I'd offer $150 and he'd take it, I don't know what the CL markup is on transmissions. Maybe he'd take $100...I guess I could offer.