If you're paying $10/month for a domain name, you're paying too much!

Richard Stallman does not insist that everything has to be free of charge, see https://www.gnu.org/philosophy/selling.en.html. It's a common enough misconception, and in reality nearly all free software is also free of charge (sometimes with a paid support plan).

A domain name is also much cheaper than $10/month, it's closer to $10/year. Oh and for FastMail, you get a discount if you pay multiple years in advance - the price for n years is $10 + n•$30

I'd make the statement a little more complex than the aphorism: "If you are not paying, and the system requires resources to operate, then you are the product."

Which I think strikes to the heart of why open source only ate specific parts of the world. Things that require resources to operate that users are normally happy about having in the modern world: network and server infrastructure, compatibility testing, support, security testing, UI updates.

I pay $30 a year for my FastMail account with no additional charge for my custom domain name. Maybe they have changed their pricing though, I have been a customer for going on 4 years.

To be clear, I'm not saying that the replacement(s) SHOULD be free. Only phrasing this in a way to emphasize keeping costs low.