The larger cons sometimes gain buy-in from the local municipalities, and for good reason. Think about what happens when a couple hundred people come in from out of town. They're buying hotel rooms, food, fuel, sometimes clothing, equipment, and trinkets and such. Even down to something as benign and forgettable as local usage taxes that municipalities charge cell phone companies for calls placed on local cell sites. All that money is taxable, and is paid to the locals. Picking a smaller town and emphasizing the boost in the local economy to the local authorities might provide some incentive for buy-in from them.
Also, definitely get the cash up-front. Non-refundable. If people don't show, they don't show, but no reason to eat that cost. Also, putting a livestream of the addresses online, not on youtube, but behind a paywall, will garner money from other chasers who can't make it. Then put the full addresses up on youtube a week or so later, not immediately.
From the standpoint of someone who wants to go to the con next year, I have to convey my experience this year. I couldn't go. I watched the presentations live, for free. I caught other presentations within a day or two on youtube, for free. Didn't cost a penny. This should be remedied, as it's a hole that money is coming out of, that can be plugged.