2 days notice you can get the chunnel from £44 return per car off peak times, twas very quick and hassle free (we got one ~8pm)
Stayed in a basic hostel in Calais for (I think) 65 Euros for a three person room. We camped in the Alps for as little as 20 euros a night for 3 people (one big tent) inclusive of electric but I dont know how common campsites are out of the Alps, probably still very common!
Other things to remember are the things you gotta have for driving on French roads: Warning triangle, replacement bulb set, reflective jackets, headlamp converters if you need them and also remember some of the main roads are toll roads.
Ive got a good atlas already and could borrow my friends walkie talkies and I would definitely be up for a trip to see this again.....