Peaceable Projects Inc. is a U.S.-based non-profit group that brings the vast resources of the wide world together with the ongoing needs of the people who live, work, and travel on the Camino de Santiago pilgrim trail network in Spain.
I think best value would be Ryanair Santiago to London Stansted and Icelandair from London Heathrow to Reykjavik. There is the transfer from Stansted to Heathrow and I'm not sure if the connections work out, alternatively you can fly to Heathrow from La Coruna on Iberia.
Iceland Express http://www.icelandexpress.com run budget flights from Iceland to Stansted, and also to Frankfurt/Hahn where you could change to Ryanair to Santiago. Check on connections and price for when you want to travel.