Hi Jbird , as I live very near Dover and my husband makes regular trips over the sea , my advice is if you have the time to nip over the border into Belgium , into a place called Adinkerke , then it's welll worth the trip.
If u r travelling by car it is appoximatley 40 minutes from Calais and the average price for 500g of tobacco is �40 -�50 depending on brand including drum and golden virginia.
Please bear in mind the French tend to sell stuff by the 40g rather than 50g.
So my advice is to head for Belgium if you have the time.