First year events are almost impossible to guess accurately. The organizers say they expect 3,000 people, but where is that number coming from? Odds are they pulled it out of the air and it is very optimistic unless they have pre-sold tickets.
My advice is invest no more than you can afford to lose if your sales only amount to $100. You can figure on making that much out of the guilt-ridden organizers alone even if you have bad weather and virtually no public. Beyond that, be conservative. Better to sell out than lose money, I say.