Dead easy - did it a couple of times via Speedferries when they were operating - on the French side, it's about 220 miles, Rouen is the only real source of any traffic delays, otherwise its autoroute all the way, and I seem to remember the tolls totalled about 18 euros last year. Good campsites to stop over at on the coast to the south of Boulogne on the way back if you can't manage the whole return journey in one go.
MG Mark