Albergue Seminario Menor offers a bus tour to Finisterre and Muxia. I took it on Saturday, 30 May 2015. At that time, only Saturday tours were offered, but it may have changed.
The tour was 40€ , less expensive than the prices I saw on fliers at the Santiago tourist office. The tour was well organized, with a good selection of stops, adequate time at each stop, and no pressure to buy something. At Finisterre we had a lunch stop and the guide provided suggestions on what we might want to eat. But we were free to go to any restaurant we wished.
The guide spoke in two languages, Spanish and English, and at times it seemed rushed, because by the time she finished we would have passed the attraction. She tried her best, and sometimes interleaved her statements when there was something particularly interesting.
I recommend this trip.