Asking companies to give you licenses for free is a nice idea (I would love everything for free), but you should suggest it to Microsoft. This is just a community forum.
Nevertheless it suggests that you're looking at a different hosting and licensing model than what you actually want. You can find a service provide and get access to AX through SPLA licensing model, instead of designing, managing and licenses everything by yourself.
"Microsoft comes with tons of servers" - Again, it's up to you how many servers you use and it has little to with whether you build them by yourself, have them in a hosting center or in Azure.
"...a firewall cluster active-passive or active-active cluster with less capacity in which you replace the broken firewall with a new one and meanwhile running on only one. Why can't Azure run this way?" - It can. What exactly do you miss?
"create a Azure subscription with a certain fixed amount of downtime" - That's not how it works. You don't pay for subscription, you pay for the amount of time and resources you actually consume. You're completely free to shut down servers when you don't need them and than you don't pay for them. This is a very important piece that you don't have in your calculation.
"SLA response time to fix a broken server" - Fixing a server in Azure means simply deleting it and deploying a new instance, so it's usually pretty short time. I'm not sure what you expect from it.
