Dragonlily,
The bus route would be Muxia to Cee to Santiago via Monbus. Here is their Spanish website >>
http://horarios.monbus.es/
Extracted from their timetable for July 1
buses leave from Muxia for Cee at
7:30, 10:30, 16:30 . Journey takes 45 minutes
buses leave from Cee for Santiago at
7:20, 8:40, 12:05,15:20, 17:05, 19:20 . Journey takes 3 hours
In Santiago the Galicia Tourist Office at 30 rua de Vilar near the cathedral has a good free multilingual list of all services including the buses along the route Santiago>Finisterre>Muxia route. Their muli-lingual staff is very helpful.
From Santiago there is a RENFE train which goes everyday to Irun/Hendaye which is the Spanish/French border. This leaves Santiago about 09:45 am and arrives at the border about 21:00 pm. In Hendaye you can get the SNCF train to Bordeaux
The RENFE train needs reservations. It is easily booked directly at the rr station in Santiago. As long as you are NOT traveling at a peak time such as a holiday you should have no trouble booking this train two or three days before you wish to travel.
For more info here is a RENFE timetable link in English. >>
http://www.renfe.com/EN/viajeros/horarios.html
Here is the French SNCF timetable. >>
http://www.voyages-sncf.com/
Good luck and Buen Camino,
Margaret Meredith