Interesting observation - the pricing stays constant at $21/user/month till 2999 users. It changes to 'Contact Us' zone after this.
On the other hand, Atlassian's enterprise offering, Stash, has a different pricing structure with only a one-time payment. Infact, for 2000 users, the upfront costs are 48K versus Github's 2000 user pricing at 500k per year.
I wonder about this large discrepancy in pricing structures between two kind-of-close competitors..