Don't migrate to Git. "Git is pain" for hg-users
You can try to read about different hg-hosting
own instance of SCM-Manager locally
free or paid Dogus on Cloudogu EcoSystem
In addition to the existing answer, I wanted to point out an alternative that has just recently "joined" the market.
How suitable this is for you, depends on the level of private your repositories were on Bitbucket. I know they were offering non-public repositories, if that's what you mean.
If you are looking to host your FOSS project publicly foss....