I have never been to a dyno event (and I have been to both individual for my car, and national ones like a Texas Supra meet) where it was mandatory to prepay. I don't know about Brian, but should I even run a group event, I would prefer prepayment.
I also want to show up and know when I will be dynoed so I don't sit for 7 hours waiting to be picked last like when I was in grade school on the play ground. No one wanted the skill less white kid.
Oh and Ben, take your damn Christmas lights down!