The Pittsburgh Port Authority bus is the cheapest way to get around, though it is at times inconsistent. We recommend using the Transit app to figure out what line to take, and the Ready2Ride app to pay for tickets. However, depending on where you are staying, you may need to find another means of transportation.
The 28X bus takes you from the airport all the way to CMU for only $2.75 ($50 for rideshare)