I'm really sorry to hear about the health problems and medical bills you've had as a result.

To lose your grandmother just after christmas must have been awful too.
Have you tried talking to the church/hall about what's happened? If not, it's probably worth giving it a go. You may find that they are sympathetic to your situation and they may be able to bend the rule. There's still time for them to fill an August slot now, so the sooner they know the more likely it is that they will help you. I know the hall is a business and needs to make money, etc, but when they hear about what's happened to you I'd certainly hope they'd do everything they could to help you out.
Nikki's suggestion also sounds good - but you'd probably better check with the hall first to make sure you can go ahead and find someone to fill your slot.
Good luck and I hope you manage to sort this out soon. I hope that your health improves very quickly too.
x