If it is raining and you egg a car, will there still be damage? How much is it to fix the damage if any?

yes, if the egg ends up on the car and drys.

Depends on the value of the paint job
2000 up at least to repaint a car

Plus of course criminal damage to property, fine, even detention ( assuming you are a child since grown adults should know better)

Eggs also damage the rubber sills around the windows... a senseless thing to do.