Lille.............. friday/saturday ........... in the new year, leave silly early in the morning, (cheap ferries and lots of noise) go for a drive around via belgium maybe, then go to the hotel in Lille we went last year, following day take a long drive to calais for shopping and come back late the following day, (cheap ferry again).
I reckon with ferries and hotel approx £100, allow £100 for fuel plus whatever you need to spend, job sorted
Just an idea