"Reasonable prices" is only fair compared to, for example, Oracle's gouging. It's not that MS has actually reasonable support pricing, just that ELA maintenance has become a cornerstone of most CIO's IT budget so there's no real incentive to do anything differently. I think the more important factor here is that MS sysadmins are a dime a dozen and the ramp from supporting an on-prem data center to "Azure Cloud" is a lot lower than learning something brand new.