I only really know about Brittany ferries- this route is pricier than eastern routes. If you do go with them:
Cheapest day is Wednesday. Most expensive is Friday, followed by Saturday.
If you want to go overnight, Caen is cheaper than St Malo (but the times feel worse, on later, off earlier). You aren't forced to get a cabin like some ferry operators, some folk spread a sleeping bag in the reclining chairs section and showers/toilets are available and I think free. A cabin for 4 fits the 5 of us ok.
Afternoon from UK and morning from France are cheaper but you may need to factor in a stopover near the port, although there's plenty of choice France side. You can go out via one port and come back by another.
Their site does allow a bit of looking around so play with days/times. Prices are cheaper now, like airfares they do rise later on. Joining the club voyage scheme (£140) can get you 30% off ferry, and some other benefits but it can work out not worth it for just 1 year if you don't plan to use it again. Or someone with a membership can share their code and you can get 10% off ferry price (I have one, if you would like it please PM me).
If you do go via eurotunnel you can use Tesco Vouchers - making it excellent value. If you have a credit card you can get a Tesco one and rack up points where ever you spend and collate them towards the cost.
Look at the times. We travelled late at night or very early morning one but it was years ago. If you are looking for camp sites the French girl at one said to look for Castel Camping as they are the better sites in France. We loved camping there. We went with Eurocamp and usually did split sites. You can even stay for one night. We used to stay a night in Normandy and then travelled on to wherever Brittany ( southern), Loire, Vendee etc funny we were just saying last night what great holidays we had with the kids over there. We had our own tent at home but couldn't fit it, luggage and four kids in the car! Have fun!
Thank you - I didn't expect to get so many replies!
Unfortunately it looks as though the cheapest routes (i.e. East coast) are the least convenient for us. It would add hours on to our journey.
Bower you've correctly sussed me out as a notice camper! I'd already been looking at Castel sites as I had heard they were good, so it's nice that you've confirmed it.
prof thank you so much, that information is massively helpful. We will probably use Brittany ferries as they are the most convenient for us. I had no idea about the cheapest days /times though, so I shall now investigate further armed with your information. And a code would be amazing - thank you so much. Will pm you.
I agree that eurotunnel is more expensive for us, but we have a caravan. P+O always seem cheaper. Prof thank you so much for the code. As it is it was cheaper to go through the caravan club as certain brittany sailings have free caravan crossings.
Worth looking at Eurocamp independent for cheaper ferries (sometimes) We find the early morning/evening fastcat from Cherbourg much better value, but we are only about 90 minutes this end to get home so works for us...lots of people seem to fastcat in evening then travelodge in Portsmouth services...
The Calais boat crossings are always cheaper than the tunnel, but obviously the tunnel is quicker. It is well worth looking at Newhaven to Dieppe which can be a lot cheaper than Brittany Ferries in high season. If you know anyone in the BF loyalty scheme they may be able to give you a discount.
You can get 20% off Brittany Ferries crossings if you book holiday accommodation with www.holidayfrancedirect.co.uk so you could add a night in a B&B to your holiday to get the code if the numbers add up?