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