Offer financial assistance and free tickets
Tickets aren’t the only cost of a conference: you also need to pay for travel, accommodation, food, and time away from work/home. Be ready to cover those costs as well.
Have a budget for financial assistance grants, so you can contribute to some or all of those costs. This expands the pool of people who can potentially attend your conference.
How you allocate those funds is a tricky question. Personally I prioritise contributors (speakers and volunteers), then first-time attendees, and I’d want it to help as many people as possible – but different events will have their own priorities.
Some attendees will be able to pay out of their own pocket, and be reimbursed after the event, but not everybody’s cash flow can support that. Think about if/how you can pay advances before the event starts.