We had a nightmare last year trying to pay our tolls on the A22 motorway in Portugal. The machine at the border wouldn’t accept our cards, we tried buying prepaid cards and registering them, but that didn’t seem to work. After three different attempts at registering prepaid cards we gave up. No doubt there’ll be wanted posters at the border for us this winter.
We now have a Bip & Go tag, which has an English website, you can check your usuage online and it can be set up to work in France, Spain, Italy and Portugal. We live in SW France so it’s very useful for us.
As others have said a lot of motorways have toll booths, so it might be worth researching the ones you’ll be using.
Hope the move goes well, we’re still debating if we should head further south.