From the center of the village in Patara (aka "Gelemis"), minibusses regularly drive past the ancient ruins all the way to the beach. Often, pension owners are happy to drop customers off at the beach as well. I wouldn't recommend the walk- there is minimal shade.
It's easy to get a bus (most of the way) to Patara. Unfortunately, nearly every dolmus running between Fethiye and Kas (or even Antalya) will leave you at the side of the highway, about two kilometres from the tiny village known as Patara. Taxis are always there to meet the bus, or other minibusses will leave when they think they've got enough passengers to make a profit. Of course, you could also walk (I might have considered it had I known it was only two kilometers, but upon arrival I had no clue how far away the village was). Regardless, you'll probably find yourself paying almost as much to get from Fethiye to the Patara turn-off as from the highway into the village! Alas.