Last time I did it in the car was about £50 each way - Calais to Avignon
the ViaMichelin website does driving directions and toll charges as mentioned
I used a debitcard at every toll, never had to use cash
If you're a real hero, you can do it overnight in one go
The stretch past Lyon gets VERY busy in the summer
Once you factor in the cost of petrol, coffee, tolls, tyre wear, etc. you might want to think about motorrail, although this can be expensive