You can advertise it as a Big 50 and if there are three shooters that want to shoot the full 100 go ahead and let them.
It is one shoot. The shooters shooting 100 pay the $3.00 and everyone else pays $1.50.
They do not pay twice.
Just make sure that there are three shooters for each.
You can't have 4 shooters shooting the 100 and two shooters shooting the 50's, you must have at least three in each. If you would say that one of the four shot 50 with the other two the girls would never be able to divide that.
Send it in as one shoot.
Put on the financial that you had 4 shooters shooting 100 @ $3.00
3 shooters shooting 50 @ 1.50 for a total of $16.50