You certainly don’t need much toothpaste to do an efficient job. The advertisements from toothpaste manufacturers show the toothbrush to be completely covered in the stuff, but a dab the size of a sunflower seed is sufficient.
I’ve run into folks like this a number of times. It’s funny how they can’t scrape together 3 bucks for a year’s supply of store-brand fluoridated toothpaste, but somehow there is money in the budget for vapes, tattoos, multicolored hair dye, and weed.