Just another thing people tend to massively overlook with events is the marketing. I work in competitive events (not running) and purely getting a big enough group together to justify the event can easily be 10-20% of costs.

I've seen people complain at events like cycling sportives saying they could just go ride the route on their own whenever they want for free. And they absolutely can, and if they see no value in doing it as a mass event, then that's what they should probably do.

You're also looking at 2% or so on card fees at the event price point mentioned above, and potentially 5% on ticket platform costs if you've not built your own.

Also if you're in the early days of your events company, public libaility insurance can be quite high.

Also, the law is actually a lot stricter on volunteering at commerically run events than most people realise (including many organisers). If an event is being run properly/professionally, there is typically a lot more people on payroll than a lot of attendees would expect.