Sung Shan airport is in Taipei (the city) so if that's your final destination, a bus or a taxi from TPE is your best bet. If you're transiting from TSA to another domestic Taiwan airport, then why not find a hotel closer to TSA? not only will there be much more selection, but your flight the next morning is a lot closer than taking the hour-ish road trip in from TPE/Taoyuan county. The traffic into Taipei in the mornings on their two main N-S highways can be hideous.