Hi Bernie,
I'm currently living in Ponferrada and I would suggest your cheapest option would be to fly to Barcelona and take the train (I lived in Barcelona prior to Ponferrada). British Airways often has the cheapest flights (if travelling with luggage) and has a stack of flights all through the day to choose from. Typically you can get a seat for £60 in advance. (I checked randomly for 11th Feb).
There are two trains a day from Barcelona to Ponferrada, one in the morning at about 0930 and takes 9.5 hours and the other is overnight (2230 to 0630). The overnight train is a fully reclining seat or a bed. Again in advance (Again I checked for seats mid Feb) and you can get a seat on either train for 30€!!
If you take the daytime train you will of course be closely following the
Camino Frances. If you take the overnight train then you can set off walking immediately and don't have to stay in Ponferrada.
And travelling via BCN also means that you can take in the stunning Sagrada Familia.
My second option would be Madrid and catch the bus (4.5 hours) - there are two different tariffs, the more expensive (called 'supra economy') one is for a more direct bus and also more comfortable seats (more legroom) which is important for me at 190cm tall.
Hope this is helpful and good luck in your plans,
Buen Camino
Nick