Adobe Experience Manager is an enterprise level collection of server apps - you need a Windows or Linux server to run it. The cost of the server is very small compared to the cost of AEM. The price is "on application" and by negotiation but expect it to be 5-6 figures (US dollars). Often board level approval is needed, but it is aimed at the whole enterprise, not just making a form. (If your question is about AEM Designer, rather than AEM Forms, then there is a cheaper answer; however the forms it makes are OBSOLETE if you do not use the full AEM forms server app).
XFA forms (also called Designer forms, AEM forms) were going to be the future. But then
- all the big software makers made their own PDF viewers (Google, Apple, Microsoft etc.)
- they didn't bother with XFA
- even Adobe themselves didn't support XFA on mobile devices
I consider them dead for delivery to "unconrolled" end users (i.e. where you cannot dictate the software used), though big form makers like the IRS are still using them.
What Adobe expect is that people working with XFA use a server component that converts PDF XFA forms into HTML5 forms dynamically. This may work well, but I don't have the six figure budget needed to try it out.