I completely agree with all the comments that suggest a time-based licensed or paying per major version/updates. But have a small suggestion.

In addition to offline functionality, can there be any type of online functionality built-in as a convenience? I’m thinking automatic backups when an event ends, sharing results to a portal for competitors to log into later, etc.

If there is, you can use a hybrid model and offer those as a subscription with a fixed license or (depending on price) a more expensive monthly that will bundle the fixed license.

Good luck!