Ayaccio Airport is about 5km east of the city itself, so it's a good idea to find out how to get from the airport to Porto Vecchio before you fly out.
To get to the city's bus station, you can take the airport's special shuttle bus, which regularly operates such transfers. The fare is 4.5 EUR. The trip from the airport to the city takes no more than 15 minutes, and there are plenty of mini-buses between Ajaccio and Porto Vecchio.
You'll already be on an impromptu excursion when you decide to take this trip, as these intercity buses pass through other major, extremely scenic resorts.