How much? I know it's undisclosed but it would be very interesting. Hopefully someone leaks it. The rumor was Miguel told MS to "F*#K Off" when MS presented him with an offer many years ago. This lead to CoreCLR being open sourced and Visual Studio Code being built. I'd like to know if by undermining parts of Xamarins business they were able to get them at substantial discount - especially with the tech industry down…
I'd almost be surprised if there were previous formal offers as I'm pretty sure the discussions between Miguel and various MS folks, especially Scott Gu, were frank, open, and mostly trusting. You don't throw out formal offers if you have Xamarin openly talking through why they don't feel the time is right.
My take is Miguel and Nat have always been "do right by the technology first." They danced the line with mono and old MS. They then made a compelling step towards where MS would head a few years prior to MS being able to start showing progress in that direction.