Our intention was to create a experience builder app (that would include custom widgets) that would be published on ArcGIS Online (thus by-passing buying access to web servers). This app would then be accessible by third party users. These user's would be provided with ESRI accounts, so that we can allow access only to them and not just anyone. From your very helpful responses, I understand that buying access to servers from a cloud provider is a necessity. After we have access to servers, we can host the experience builder app there (according to the link you shared). If you don't see any problems with what I explained, I will go ahead and accept you first response/ close this thread.
Thanks!