Probably a bit late now, but this is a very risky business with all your eggs in one basket.

I would not consider promoting such an event unless and until your costs are covered regardless of the number of tickets you sell. That can be achieved better by sponsorship than investment in my view.

However, a safer option is to crowdsource subscription.

Describe the event, find or create a community to get behind it. Set a target amount, after wish you will confirm the event. Allow people to pay for tickets in advance at discounted rates. Put the funds in Escrow. Tell people that, if you fail to reach the "Go" target, they will have their money returned.

Good luck if it's not too late.

Mark