Family of five, one income, I homeschool the kids, and we spend $25K a year not counting the mortgage and including health insurance and travel(US camping and visiting relatives). We're in an average COL area with a 1500sq ft house, two cars and soon to be camper. Without the kid expenses, we'd easily fall somewhere in the 18K a year range. If we downsized the house(in a scenario without kids) it'd be in the 15K a year range. Although I suppose we'd travel and go out more if we didn't have the kids, but not much more.
When we lived in NJ(medium-high COL, Southern) a few years ago, I calculated our bottom number for family expenses to be around $25K without mortgage or travel but with health insurance. So we're doing better here in an average COL area, even with a home twice the size of our last one, since our $25K base now includes a generous $3600 a year camping budget.
It helps if you actually love simplicity and feel overwhelmed with all the stuff and stimulation outside your front door like we do. Staying home and baking, reconstructing something old into something new, or reading library books is practically free as entertainment.
A budget can only go so low as your personal level of deprivation. Once you hit that level you bump it back up a notch and that's your bottom level. Different tolerances for different personalities so it's not always very helpful to compare to others.