Unfortunately, you may be disappointed XD, in France, they do "on the spot" fines. This is where they pull you over, give you a ticket, and expect you to pay in cash on the spot. If you don't have the cash on you, they will escort you to the nearest bank to get the cash out. I go there quite a lot, also, if you are on country roads, the speed cameras are grey and don't stand out, and they aren't always sign posted like here in the UK. I have also seen police with radar guns hiding behind signs and buildings before, so watch out.
Don't wanna sound like the fun police, but it's worth being aware of. Don't forget all the stuff you need to have in your car on the continent too, if they stop you for speeding, they will ask to see it. Ask me how I know...