In my experience, the multi-city tickets from Canada do not save you money. You are better off just making a good estimate of how many walking days + how many rest days + how many sightseeing days you will need, bite the bullet and buy a return ticket. Unless you have a reason other than the camino to go to Valencia, I would suggest Madrid. Train and bus fares from Madrid to wherever you are starting are very reasonable.
I am currently tracking the price of my ticket from Toronto to Madrid in April. Currently it's at $780.
Best of luck - others here will also provide you with useful information.
Buen Camino!
Lynne, I don't think that multi city means a ticket that goes into one city and returns home out of another city. I think that's an open jaw ticket.
I think that the "multi-city" option on kayak, orbitz, etc, refers only to a continuous journey, such as Toronto-Madrid-Sevilla-Barcelona-Madrid-Toronto.
But if you want to go into one city and out of another city, that's not a "multi-city" ticket, that's an "open jaw" ticket, and I don't think it's available online. You have to buy it through a person on the phone. I am not an expert on travel like some others on the forum, so I hope they will correct me if I'm wrong.
When I priced the open jaw last year for US-Madrid-Valencia with return from Santiago-Madrid-US, I found it was only about $120 more than a round trip ticket to Madrid from the US. It also meant that I could get home to the US in one day. My flight left Santiago at 9 am, I connected in Madrid and went on. If my international ticket just takes me in and out of Madrid, I would never risk buying a one way Santiago to Madrid flight on the day of my departure because if my flight to Madrid is delayed and I miss that international flight, it's not the airlines' problem, it's my problem (my husband learned that the hard way and it was expensive.) But if my international ticket just starts in Santiago, then I am guaranteed I will get home on my ticket, no matter what the delays may be, it will then be up to the airlines to rebook me.
$780 RT to Madrid seems very cheap to me. Do you have your dates yet? Buen camino, Laurie