I'm a bit of a cheapskate, so I think a couple hundred a year for the family would be acceptable. That includes my parents, brothers, nephews, nieces -- I give out accounts under our domain to any blood relative with the same last name. Not a huge number, but it's like ~16 accounts. Only four or five that get any substantial traffic, but the rest are still perfectly valid individual accounts. At about $55/year/account for ProtonMail (if I looked in the right place; prices were in Euros), it pushes a thousand bucks a year. For email, that's simply more than I want to pay. I'd go back to hosting it myself on a Digital Ocean droplet before I'd spend that much on it. But ... I don't yearn to be in charge of security and tech support again ;-)