Pittsburgh does not have a subway system. The 28x bus from the airport will drop you at the University Center ($2.75 each way).
Taxis and hired cars are available for the 20 to 30 minute drive (baring traffic delays). Prices range from $45 to $100.
If you want a car service (~$80 one way), send an email with info to Theo at Corporate Sedan, tell him you are with Prof Salisbury's conference. They have a van to make it economical if you are arriving with several colleagues. Corporate Sedan Service corporatesedanservice@yahoo.