Dave
St Tropez is quite a long drive. There's no point "killing" yourself to travel down in 1 day. If you arrive in France early AM, set somewhere like Clermont Ferrand as an overnight stop. Auto Route tolls will cost you a fortune. Last time I went down there on my bike it was free

but speaking to a cardriver down there I seem to remember him telling me it was about £250 one way ? It'll be worth checking on.
Have you ever cleaned boats B4? Make sure you have immaculately clean deck shoes. Portable HWE? They're 110volt en France and you need to check how many amps are available on the quay side too. There may not be enough. If you're T/M then you'll need to check water availability and disposal facilities. You definately wont be allowed to dump waste overboard. A van may cost more in tolls too. If the berth is just outside St Tropez in a village called Port Grimaud, road access may be a problem. Don't forget to cost for extra liability insurance, your van may only be 3rd party, RAC European cover health cover etc. etc. Realistically you are probably looking at 5 days to do the job/travel. I would have thought that £2000 wasn't enough.
Safe and happy cleaning

Ken