A small conference does not need a big budget. It needs a venue that says yes to community events and a handful of sponsors who care about the same people you do.
The venue is most of the budget
Coworking spaces and universities are often happy to host on a weekend. Ask early and offer them a stand or a talk slot.
Keep the ticket price honest
A low ticket price with a few student places keeps the room diverse. Sponsors cover coffee, lunch and the recordings.