Just remember to factor in road tolls to your budget. I think you can find out on line. Super easy to use tho - you just stick your card in and don't need to even type in a pin. And yes agreed with biwi - roads during hold especially in august are hell. Mass exodus towards the coasts!!
We have had several one week holidays in the region and have always driven. Especially with a 1 year old, it is great to be able to chuck everything in the car and go. A lot cheaper too, and you get to see more of france on the way.
For speed on the way out the Chunnel is best - just drive up and go. No need to take DC out of car if asleep. Can be nice to get ferry on way back to stretch your legs and get a relaxed meal. I would definitely have an overnight stay to break up journey - Hotel BB chain are a nice budget option we have used, or Novotels are nice if you want to splash out a bit more. Get registered on the Novotel email list and they send you special offers - have had many half price rooms in this way.
If we were to drive it would be a one week holiday. Although 10 hours sounds like a long time, going to airport - check in - board - flight - get the luggages on hired car sounds like more work and with waiting time would take 5 hrs each way?
I suppose it depends how long you are going for. If you are making the wedding part of a 2 week holiday and need loads of stuff then driving could be good. If you are going for a weekend then flying may be better. You would arrive fresh for the wedding and have also have taken advantage of not having to buy your DC a seat on the flight.
Going to a friend's wedding in France, DS will be around one year old by then. Is it easier to drive or to fly? its a ten hour drive each way, can be split over two days, good thing is we can throw everything into the car boot. Or is it easier to fly? Will probably need to take car seat and travel cot with us which sounds like a lot of hard work if we were to fly. But then 10 hours of driving each way is also a lot of work...