In reply to ed34: I was in France for a month last summer, used the screw-on cartridges. It was always a mission finding them, and they were like 5-10 Euros a can. Think we used 5-7 cans, not entirely sure. Only used it for dinners.
Last time I was in France I camped for 2 weeks. Used an Omnifuel with petrol, total fuel cost was 1Euro 50. The last time was in Easter, so we used the stove for all dinners, some breakfasts and copious amounts of tea.
Whisperlite is a bit cheaper than the Omni, but still a very good stove. Stay away from gas; it is expensivo!