$10-$130.

A fall gravel race is technically free but they ask that you bring canned/boxed food for a local food pantry. Then there are various gravel races that cost $30-75. Then there is something like BikeMS where the minimum required amount to be raised(or just paid) is effectively $130.
There are many more rides, but I only do a couple of organized rides(besides a few gravel races that Ill never come close to mattering in) so I dont know the prices of everything around here.
From what I can see, the costs do seem to be in line with the entertainment/support for each ride.