50-50 %  with half going to charity...is that the deal?   ........

 

1) money has to be collected up front and put in lock down (how the hell would that happen?)(I'm not going by the honor system here)  

2)  I think a simple total ounce count (indicated and inferred )  would work the best  (uncut)  -and maybe a cut once guess as a backup

 

maybe there is some software or pool program out there that offers the service to hold themoney for the winner