" "- the supported versions like Redhat and SUSE are more expensive to license!"
Are they? Does anyone here actually know the facts (comparing like-for-like) here?"
It is a quite hard question. In the x86 land, Suse charges by socket. Not by memory, cores, threads or whatever. Also, a quick glance didn't show me any limits on use, number of users, load, storage or network usage.
Also, there is a steep discount if you subscribe a 3 or 5 years term.
Example: Standard support (the middle one)
One year: US$ 799 for a two socket machine.
3 years: US$ 2160,00 for a two socket machine.
5 years: US$ 3200,00 for a two socket machine.
This gives you a support 12x5, with unlimited contacts, trough chat, email and phone. It may be pricier than a basic Microsoft server. But it could be used on load levels that would call for an Enterprise Windows Server.
A 4 socket would be double this - as they charge one license for each two sockets.
As you see, not a clear cut answer - and a quite hard one to get.