It tends to run a little more when you're using hosting in a country that doesn't respect US copyright (and similarly for most EU) along with keeping your information private to begin with. When I had looked into it, it's been roughly 2x what a typical western dedicated server provider might charge.

This doesn't count the issues with a site that is very popular, from bandwidth to even simple database search overhead. If I were to guess, it's that RarBG probably spent in excess of $10k/month, which isn't much if you're a startup with a runway of VC capital or a revenue stream, it's a lot more if you're in a smaller country or don't have an excess of revenue.

Comparatively cheap because you're just handing off magnet links, but when you're serving millions of unique visitors daily, it all adds up.

I believe rarbg had many "official" torrents that they seeded. This must be part of their costs.