I've always wondered about the service industry from the past. It seems like "milk man" services were ubiquitous at one point (if popular culture and anecdotes from baby boomers are to be believed). As in, everyone used the milk man to get fresh milk delivered to their door.

My question is simple: was the cost of milk from these services comparable for the same quantity of milk one can procure from the grocery store today? What would be the difference in cost adjusted for today's dollars? I'm curious what portion of one's income families were spending on this iconic service.