I've done Eurotunnel via Tesco vouchers twice now, easy and cheap! Driving from Calais to Touquin (20 mins from Davy Crocket roundabout) took 3-4 hours each time despite quite horrendous crash on Sat morning just by La Francilienne (their M25 equivalent) and another by Charles de Gaulle airport which shut access to motorway toll road.
Have got a satnav but didn't bother using it even though I had to make my own detour. Road signs were clear enough.
Tolls cost 19.50 Euros each way.
Petrol is more expensive in France - prices range from 1.20ish Eu to 1.51eu on motorways and Disney! Diesel is cheaper there than UK I believe but as I don't buy it I wasn't really taking much notice.
Motorway driving is easy, even on a Saturday there are very few HGVs. Country road driving is sometimes more challenging, the roads we used were populated by French drivers who were always in a rush and sometimes seemed to want to push me off the road in their eagerness to get past!
If you get time and have the inclination there is a massive shopping centre next to Calais Eurotunnel for any last minute shopping or if like me you arrive to early to get into Eurotunnel site.