That's around $268 per Github user.
Now MS could have probably made a site comparable to Github for 0.1% of that cost - e.g. revive codeplex, pump a few million into the design, backend, git support and user interactions.
But it wouldn't have 28M users. That's what they're paying for. That's the hard part.
1) https://news.microsoft.com/2018/06/04/microsoft-to-acquire-g...
That seems like a decent deal for MS... Assume on average a user is an active engineer for 5 years (of course this is back-of-the-envelope and not even taking into account the growth of the field, and new engineers are likely to use Github for it's network effects).
Is the value of owning the central platform of an individual engineer worth more than $50 / year? Even if all you did was run basic ads I'd say yes - although I'd expect more services including edging in on Atlassian's turf as an upsell opportunity for MS.
All this, not even counting future value... If Slashdot is still around and somewhat valuable, Github will probably also still be around and somewhat valuable at least a decade from now.
Indeed, as cost of acquisition of an active developer, it doesn't seem either absurdly high or absurdly low.
https://blogs.msdn.microsoft.com/devops/2018/06/04/vsts-gith...