As discussed, it depends on who's running it and what sacrifices they're willing to make. It's no different than any startup, really. Some people get fully funded and pay for people, facilities, processes, professional prototype fab. Others bootstrap their companies and sacrifice most/all benefits just to get rolling. Bootstrapping is how we're mostly doing it, but expenses increase dramatically as the company matures.
I come from the hardware world, where you can choose to work for free (if you have the means to do so), but making physical things costs money. It's easy to estimate how much it would cost to build a few prototypes with mostly existing pinball parts; you can use P-ROC community examples for pricing metrics. Building new technologies and new features, like we are doing, costs a lot more and carries more risk. The flip side is that when new ideas are vetted, manufactured, and accepted, the entire community benefits, and future efforts can leverage that work/time/money-spent.
Every owner is different, and each company is different, but I think everybody can agree on one thing. Building a pinball company is an expensive proposition. Everybody doing so has my respect for taking on the challenge.