Jekyll + Github Pages / Netlify / Surge is free with subdomain. Or you could buy .dev (or anything else) for minimal price. Personally i bought 1$ .xyz domain. Its not that “costy”.
It doesn't cost me a lot of money, indeed, and I'm happy to pay the couple of Euro's that it does. GGP suggested that you shouldn't let Medium earn money over your content, though; even if that's something you care about, it's still a better deal than paying for your blog yourself.