Great offer in The Daily Mirror. Departing from Dover you can go to Calais for just £1 if you are on foot (depart after 08:25 back before 21:45). You can take a car with 4 people for £17 (depart after midday back before midnight). You can stay over night with a car and 4 people for £19, or do a 3 day trip with a car and upto 9 people for £49. You get a free bottle of wine with all car journeys as well which is nice.
You need to book by April 30th 2013 and travel by to May 10th 2013. (No travel on 13 & 14 April 2013).