Is it less expensive to fly on "one ticket" from SCQ to MAD and back to the USA? It is too late for me now, but next time I'll consider.
Good question. I think if you're flying two flights on Iberia, from SCQ -> MAD, and MAD -> US, the two flights added up could be more expensive than just flying Iberia from SCQ -> MAD -> US on one ticket.
Of course, usually pilgrims are not flying all the way into SCQ before starting the Camino. So your plan makes sense, just to do a roundtrip from the US -> MAD -> US and then figure out how to get back to Madrid after the Camino.
Recently, with ticket prices fluctuating kind of an insane amount, what I have seen some people do (and what we just did, see below) is to buy two one-way tickets: the first from the US -> MAD (or Porto), and then travel on another one-way ticket after the Camino, SCQ -> MAD -> US. This can work well, price-wise, if one of the itineraries happens to fall during low-fare days or if different airlines have better deals.
For example, we had visitors come this year over Christmas break. If they bought round-trip fares from the US -> MAD -> SCQ -> MAD -> US, the price for each ticket was going to be $3,600! They definitely couldn't afford that. So they bought two one-way tickets: US -> Frankfurt -> Porto on Lufthansa. We picked them up in Porto and brought them to Santiago. On the way home, they did SCQ -> MAD -> US on Iberia. The total for all of this was $1,800 each. Still so much more expensive than non-holiday travel, but the fare for Iberia in January was so low, even though the fare coming over on Lufthansa in December was pretty high.
Lots of details. Sorry if my response makes your head spin!
It feels like such a tedious game sometimes.