In reply to Fickalli:
I think you greatly underestimate the toll costs. I few weeks ago I drove down through France, Italy and Croatia and back again, plus side trips, and (not having done this for a few years) I was amazed at how expensive the tolls were - about twice the fuel cost. (I have a very economical Golf diesel, which averaged 58 mpg at between 120 and 130 km/h).
I paid for most of the tolls by credit card, some by cash (in France), which is NOT included in the following analysis. Checking my Barclaycard, on my return, I found that I had used it exactly 30 times to pay for road tolls alone, at a total cost (converted from Euros and Kunos into pounds) of 843.28 pounds over a 5000 mile journey (not including the cash thrown into some peage's in France).
Tolls on the outward journey cost: France 134 GBP, Italy 170 GBP, Croatia 160 GBP
On the return the tolls cost: Italy 109 GBP, France 262 GBP (the latter being the toll cost of the entire journey along the French Riviera to Nice, then almost to Marseille, and then the whole way up to Calais.)