Try using
http://matrix.itasoftware.com as a search engine. From Miami to Madrid, I'm seeing flights from $550, round trip. On Matrix you can check nearby cities and dates for departures and arrivals, you can sort the data (flights) by city, time, cost, etc. -- If you can just get across the ocean, you can pick up a cheap flight from other cities (Paris, London, Frankfurt) to Madrid or other Spanish cities, and from there travel to O Cebreiro by bus. You can even get tickets to Santiago de Compostela pretty cheap. I flew from Toronto to Paris for less than $400 round trip in 2016. You might also look at buying two separate tickets here in the US--get a flight up from Florida to a NYC airport and then flying from NYC.
-- PS You can not purchase the ticket on the matrix.itasoftware site, you will have to contact the airline, or buy it from the airline's website. The costs given by matix include fees and taxes, unlike many other search engines.