I'm a breakdown contractor and provide service for several companies (like green flag, Europe assist, Brittania etc.) I've no idea what policy costs are involved but the one thing you should check, especially on cheaper quotes, is that you are covered to get home. Every day I go to some-one who only has 10 mile recovery and can be charged as much as 4 pounds + a mile for every mile over!!
In almost every case, you will be attended by a local contractor if you breakdown abroad, so take a phrase book

Make sure you have the correct contact numbers before you go as it can take hours if you don't contact the correct department in the first place. Every cost for your recovery has to be authorised before it is carried out, and can only be actioned by the relevant dept.
Be prepared to possibly have to return home with the vehicle to follow, as often getting a non-runner onto a ferry requires a different booking
I can't reccomend any particular company as they can all provide adequate service, just a matter of cost.
Good luck with your trip:)
btw, check with your insurance company as most can offer a discounted breakdown cover with your vans policy. They're usually quite good value for money.