Bob, it depends on what is considered a business. There are retired ladies who supplement there income by doing "day care". There are normally no more than 3-5 kids so there is no need to be registered. So it is not counted as a business. It is the same as men doing auto repair or people who bake in their homes. So long as it is not more than a certain amount, it is not considered a business. Therefore there are no costs such as a separate kitchen, health codes that would apply to that business, etc. Also since it is not a business, they can pick and choose who they do business with. Some will only do this for fellow church members, neighbors, co-workers, etc. Therefore startup costs really aren't realistic if it is for a small group. Also, as you mentioned, most businesses are family owned so their is a share of the profits, not an actual salary.
Also a lot of businesses fail because that person may know how to cook or repair, but managing, setting up budgets are not something they had no forethought on until it is too late.