Ask HN: How would you book a room for an event without going broke?

I'd like to organize my first event on Eventbrite in San Francisco and I have a logistic question for those who went through this process. I'd like to break-even, my goal is not to make money on the event I just want to help people and create connections.

I'll be showing people how to build a website in minutes and how to start selling products online using the latest tools.

How would you go about booking a space for the event? I want to use Eventbrite for the invites and I can either sell tickets or make it all Free. Booking a meeting room in SF is quite expensive. So, would you book and pay for a room in advance then sell tickets? What if nobody shows up?

Thanks for any tips!