From your description, I thought it was $50 but is now way higher. It seems to be $45. Doesn't seem outrageous ... it's like going to a fancy restaurant, but you bring the food, I guess. I imagine the fee covers getting the place, post-cleanup, whatever.
With that said, I don't think it's my kind of party - I prefer bringing booze in lieu of an entrance fee, you know?
In context, it's silly, self-indulgent, mildly elitist, and ... possibly fun. Just like many of the other stupid things we do in life!