I'm planning a trip to France in a few weeks time and a friend suggested getting a tag for the French motorway tolls (to save queuing time at busy periods). I've just found that you can get a reduced price on this if you are travelling via Eurotunnel and have a booking reference or frequent traveller number - saving the €10 application fee. The link to this offer (which I note can be withdrawn at any time but seems to have been going for a couple of years now) is
http://www.eurotunnel.com/uk/travell...sanef-tolling/
Please note, I have no affiliation with SANEF or Eurotunnel - just sharing the information in case it's useful to others