I think there is only a freight ferry. The slow Stena thing is 95% trucks. The fast thing is a mix, but is pretty much the same price as an overnight ferry + accommodation (which is compulsory for the overnight ones). The day-time crossing times of the slow one are hopeless.

I took the overnight ferry in September. Came to £500 return including cabin (work paid <img src="http://www.catsailor.com/forums/images/graemlins/grin.gif" alt="" />). Very civilised way to do it. Get on board, decent dinner (included), couple of beers, and wake up somewhere convenient (then drive like a loony because the race is at 10am and they've closed the bl**dy motorway)

Going via Calais is cheaper - I've found the ferry to be cheaper than the tunnel with trailer - but there's a reasonable drive on the other side. A reasonable way to do it would be to get a late ferry/tunnel crossing, find a Formule 1 near Calais (all of £20 for a room) and finish the journey in the morning.

(edit: Mark - you said P&O - did you mean that? I thought that only Stena did Harwich -> Hook)

(edit: Oh yeah, one of the less well-known advantages of the F16 class is that packed sensibly, they'll fit inside the 6m trailer length bracket on the ferries...)

Paul