I'll offer this: I'm migrating to Proxmox from Citrix Xenserver. I used to subscribe to XenServer, then they changed the licensing procedure (I needed to run a new VM to handle licensing) that I couldn't make work and there was zero support for getting it installed even though I was paying something like $1,000 per server for licensing. Then I noticed that everything worked without the license server, so I forgot about it.
Now Citrix is downgrading services for everyone that's not buying licenses, and is taking away features (like HA) that people have grown dependent on. Citrix has worked fine for me, and I could license it or use the non-HA version (it's not like I need HA - I just like it for when I go on vacation), but I've lost faith in the company's management of the product. So I'm moving before I need to.
I mention that to say this: Proxmox is a pretty impressive product, and the entire thing is open source, meaning the developers are competing against themselves, and they're not requiring anyone to pay anything unless they choose to use the stable repository.
That's the business model. That's what they think is fair. It sounds fair to me.
So, Proxmox needs to pay salaries, and maybe help out with retirement, and buy hardware to test on, and hire more people if they're going to increase features in new feature areas, and the folks running this company would probably like to get more back from it than an investment in bonds, and...
Proxmox needs to pay its people and make money in order to prosper and be something we can depend on in another ten years, otherwise they'll be bought out by someone with lots of money and everything will change (and probably become much more expensive or unobtainable.) Price your 40-node cluster in Xenserver or VMware licenses and see what that costs. That number is the value that the market assigns to competent VM hosting platforms. Which Proxmox now is/aspires to be, depending on how you value things like educational options and third-party documentation and third-party tools.
What does a competent developer get paid? If you don't pay someone who's good a decent raise they'll move somewhere that pays them more. That's rational. How much does the owner of a company need to make in order to be able to resist a $x0,000,000 buy-out offer from a big-boy who wants to incorporate some cool tech and remove a low-price competitor? Enough that they don't feel like they're not getting a fair return.
Where does that money come from? Licensing. Service contracts. That's it. Those are going to increase higher than inflation.
And as those prices increase, as long as they're lower than Xenserver/VMware/HyperV you're getting a good deal. Get too close to those prices and you'll have a hard time getting bigger customers who could instead buy the thing that's always talked about in Infoworld.
That's not good or bad. It's the way of the world. When I was running 5 old servers to host my sites and couldn't afford the licensing with Xenserver/VMware I found it cheaper to buy new hardware and reduce the licensing cost. It might be worth looking at that.
Or, you could reach out to the above contact point and request a discounted long-term contract, and if you're a non-profit or something plead your case.
But getting upset because the price is increasing? I don't think you're seeing the entire picture.
(Yes, this is coming from someone without a current contract. I'm still testing this platform to see how well it works for my intended usage.)