Not booked my ferry yet, wasn't sure which route to take, but just re-checked LD Lines and I got a price of £167 for a car + 2, going out on the 14th coming back on the 19th, no cabins left tho, but a lot less than Brittany.
I usually go Dover-Calais, but at 13mpg it looks like Portsmouth-Le Havre will work out cheaper with the shorter drive both sides of the channel!
Geoff