Though it refers to IAD this thread might help:
http://www.flyertalk.com/forum/travelbuzz/332587-question-about-supershuttle-rates.html

I do remember a sign inside one of the vans in SFO about max 3 or 4 stops. Only problem is waiting at the airport. They might not go unless they get a minimum number of passengers. In the case of SFO they might circle the terminals a few times.

A taxi ride to downtown Pittsburgh is around $45.