About Prime 11 purchase.

According to the (nearly 5 year old) answer of @Fred_Kohlhepp  here (-> Home Use License - PTC Community) there is (or was) a home-use license for about $300 per year.

I have no idea if this still applies and where or how you would be able to buy that license.

Another suggestion in this thread was to take a course at your local university and acquire the cheaper student version 😉

I, too, could not find any information on purchasing a home-use license in the maze of the PTC website.
There is a knowledge base article about home-use licenses Article - CS58240 - Home-use license information about Mathcad and Mathcad Prime but from this its not clear to me if the described kind of license isn't bound to a regular license (so a company with a regular license could give the employee the opportunity to use the software at home as well). I attach a picture of this article as you probably will not be allowed to access the knowledge base.

I found some information about a "PTC Mathcad, Professor licence subscription" for £ 258.00 at the website of a UK reseller. 
PTC Mathcad, Professor licence subscription - Mathcad Alfasoft

So its looks that the kind of license described by @Fred_Kohlhepp  still exists ... somewhere ...
I also found a "Mathcad Online Shop" (!?) which sells that very license for € 386.75. -> Mathcad Professor Licenses
Still not a bargain, especially when you consider that it's not a purchase, but only a 1-year subscription.

I am not sure if @DJNewman , who according to his signature line is managing all PTC Mathcad marketing, could shed some light on this issue.