DavidF said:
Piru,
Also check out Iberia - depending on the day and time you can fly roundtrip from Madrid to Asturias for 57 euros (of course you're probably not flying back from Oviedo but round trip fares are usually cheaper than one-way). Or you can fly back from Santiago and if you price it using "multiple destinations" it can be as low as 58 euros total (i.e., average of 29 each way). I'm planning on doing the Primitivo in August and got a flight from Madrid to Oviedo and back to Madrid from Santiago for about 70 euros total.
Buen camino!
I wouldn't choose the plane for that travel. The airport in Asturias is quite far from Oviedo, so after arriving you have a quite long travel by bus to Oviedo.
About the Camino Primitivo, is about 14 days if you take the Oviedo-Grado-Salas-Tineo option (20 km each). But, if you prefer to walk etapas a bit longer you can walk Oviedo-Cornellana-Tineo (30 km each). The albergue in Grado is not exactly in this town, but two km later, in San Juan de Villapañada.
About Lugo-Santiago, if you take the Palas option you can walk it in just three days (36-26-39 km). So, the whole distance can be walked in 13, 14 or 15 days.
About Santiago-Fisterra, it's quite normal to walk it in 3 days (Santiago-Negreira-Olveiroa-Fisterra). But, you can choose a 4th day staying in Corcubion (9 km from Fisterra). And, you can take another option, to continue from Fisterra to Muxia.
So, many different options, choose the one you prefer. And, remember, you only can be accepted in the albergue in Fisterra if you have walked to Fisterra, the bus is not a valid way for that.
Buen Camino,
Javier Martin
Madrid, Spain.