Good day Alex - @Alex-5623 ,
If I understood you correctly, then you compare a server operating system (Datacenter) to a user operating system (Windows 10), which does not make a lot of sense usually, since these OS are pointing for different use. It is like comparing Dog to a Cat. If you are "Dog's person" then you should not select a cat, and if you need the feature which come with Windows client (like Windows 10) then you should not select a server OS, and vise versa.
Recently I decided upgrading from the B to F series is necessary. After looking at the pricing the Windows Datacenter is MUCH MUCH more expensive on F than it was on the B series.
My 2 cents: This make sense to me, since B for example usually does not fit for servers and is used mostly for developing and testing or very small VM, while F bring you a common VM for production server + features which are not come with the B options.
If I create an F series VM running Windows 10 Pro instead of Datacenter would it be cheaper?
As much as I noticed and know, all Windows OS cost the same.
You can simply start to create new VM in your subscription in order to get a good estimated of the real price for your specific subscription. You do not have to finish and actually create the VM
Or as Dave suggest, use one of the online calculator (as you can see, there is only option to select Windows OS and not to elaborate the specific windows OS)
Check this calculator, I like it more for cases I need to compare the price for different size:
https://azure.microsoft.com/en-us/pricing/details/virtual-machines/windows/