Fees can vary from FREE to expensive (but well-worth it)!
Lots of events are casual local gatherings or short 1/2 day or day-long events and are free to attend.
Many are “free” but you are covering all your own, incidental costs.
Many have a nominal fee to cover the venue or campsite or special event or feature shared by all.
Some special fees might come with a fancy catered dinner, an excursion, transportation, etc… and it may come as a packaged fee or a la carte fees.