$15/m sounds a bit much to me for a custom domain. You can get the same for $7/$9 on GitHub if you want to make the corresponding repository private (I know, there are other differences too e.g. Jekyll modules). GitLab can work, but it was extremely slow for me (not the hosting but the UI).

My question is that is there a free alternative for Jekyll hosting with custom domain from private repository? I loved aerobatic, but it is too much for me for my hobby sites (3-4).