yes, GitHub Enterprise Server is not free. And yes you pay a license fee per user per month, billed annually, and the minimum license purchase is 10 users at something like $21/user/month. Microsoft discounts you qualify for will bring that down. You pay because you get support. You won't need it often, but when you do, you really need it.

It is easy to administer even for 15k users, and mostly it takes care of itself if you give it enough RAM and CPU for all the activity.

Downloading the virtual hard drive image from GitHub is easy and decrypting the code inside is borderline trivial, but I'm not going to help anyone do that. I've never had a need to do it.

As a server product it is good. I recommend it if you can afford it. It is not intended for private individuals or non-profits, though. It's for corporations who want their code on-premise, and for that it is quite good.