I'll go against the flow here:
Eurocamp - very expensive for what it is. It's a tent or a mobile home the likes of Haven use - and charge a lot less for.
Cote Opale (west of Calais) superb beaches, but I'd hazard a guess at not that great for cycling -terrain quite rolling but not interesting. Also possibly expensive as the area includes Le Touquet, which is the area that Parisians tend to go to for short breaks and weekends, so accomodation, eateries etc tend to be a premium. We went to the area at easter a couple of years ago, and the roads were very busy locally in the Le Touquet area even so early in the season.
For a sunny beach type holiday then I'd suggest Charente Maritime (department just south of Vendee). Better weather, maybe slightly less busy than Vendee. It does have good beaches, just need to look for them (St Georges des Didonnes, a few km south of Royan, is a cracking golden sand beach) and often gets the right winds for kite surfing etc.
Ferry crossing wise, anywhere in western france is best done with a longer crossing, Portsmouth Caen is a good one, not cheap but dover-cal will usually mean an extra overnight stay thrown in somewhere in the journey.
France has become generally more expensive in the last 3 years, even fuel, despite their lower taxes, isn't going to be much cheaper than here, soemthing that needs to be factored in. Given an option use the autoroutes, direct, fast, less congested than UK motorways, tolls are not that expensive.