Not sure of your budget but here is what I do;
Start with finding a cheap flight to anywhere in EU. Once found, open another window and look at ways of getting to the end point from the end of first flight. Remember, this is an adventure.
My first trip, I left home, got on a city bus to a point in town where I could catch a train to Montreal. Time is important for connections but I was happy with taking a few extra days to get where I was going. Montreal to Dublin via Rejkavik with WOW Air, cost was C$419. Spent 10 days in Ireland then took the ferry from Dublin to Holyhead, Wales, overnight in a B&B and then train to London for a couple of days.
I planned to spend two days in Paris but as there had been a terror incident just a few days earlier, I started getting antsy and booked a C$200 flight from Stanstead to Biarritz with RyanAir.
Upon arrival, I walked out the airport doors, approached the first four pilgrims with backpacks and asked,"St. Jean?" We filled a cab, paid 25 euro each and an hour later, we were in St. Jean Pied de Port. One had been there before and showed us the Pilgrim Office and where to stay overnght. This got me on the road a full day ahead and made friends with four Pilgrims before starting the Camino.
On the return, I booked Aer Lingus from Santiago to Dublin EU200 and then Westjet to Toronto for C$450.
Down side: Gave up tent pegs bought in Dublin at Stanstead but was gifted some at Orrison by an Australian Pilgrim. I still have those.
In 2018, I will look at other possibilities, this time from Toronto as I have seen rates as low as C$340.00 from Toronto to Lisbon. Stops can include Madrid, Barcelona as well as Paris. There may also be some cheap possibilities by using USA based air flights, ie Seattle to Paris or Madrid?
Now, once in EU, bus and train transport are usually very economical and very flexible. As an example, I had to cut off my first Camino before Pamplona. I boarded a bus from Zubiri to Pamplona, then to Bilbao then to Santiago in about 20 hours, including transfers. It cost 72EU.
I am certain, even from Van that there is a good combination out there for you. Charter One Way Flights may work best for getting there and wing it on the way home, possibly? It is really the only way to keep return date open and flexible.
