Just returned from a trip to Spain and France. Here are a few numbers that may be of interest.
Avg lowest petrol cost per litre: Spain 1.328 euros (£1.20) France 1.489 euros (£1.35) these prices were found mainly at Supermaket fuel stations. Saw prices as much as 10 - 15 cents higher in Spain and 15 - 20 cents higher in France.
Travelled by ferry from Plymouth to Santander on the outward and Cherbourg to Poole via High speed ferry on the return. Ruby(2.1 Westy Atlantic) and 2 adults + 2 berth cabin on outward cost £587 return.
Campsites we used, ranged from 13 euros inland to 29 euros by the coast per night in Spain and 15 - 35 euros in France.
In total we travelled 3622kms(2250mls) using 415ltrs(91gls) averaging 11.5 litres per 100 kms which equates to 24.6 mpg.

Hope the stats maybe useful
Steve
ps only used the peage once from Logrono to Zaragoza, cost 12.75 euros(£11.50)
