The later you leave it the dearer it gets.
If you really want to do Calais bear in mind Norfolk Line to Dunkirk there are no cars on their ships and normally cheaper and a bit further up the coast northwards.
Also it will cost you a lot more in Petrol over 570 miles return from Calais and you're knackered when you get there plus on the Sunday you have a hell of a long way to go to the ferry.
See the comparisons in Region 13.
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