I've tended to drive & ferry across to France on Wednesday evening (6pm sailing)
Then have a nice blast down on Thursday, and usually returning Monday morning, but driving half way back through France on Sunday evening.
Again, iirc, the price was around £250 for ferry, camping and grandstand seat with access to all round the circuit. Fuel was a bit more.
Oh and there's food, and for some, I believe they have a few beers too.
Anyway, it's still cheaper for Le mans 24 Hour than a granstand seat @ Silverstone on race day for the F1 (for 2 hours of racing?) Well nearly.