There are several daily bus connections directly from Catania Airport to Modica. So if you don't want to rent a car at Catania Airport, you can easily get to Modica by bus, then hire a car locally for the days you want it. There is also a railway station in Modica, with a VERY slow train to Siracusa. Otherwise the local bus service is pretty good, and reliable. There are several daily bus connections with Palermo too, which is about 4 hours away.