In a long run it'll probably not be a good idea to have a custom help for each of your "many pages", as you said. Some reasoning at the end of the answer.
SharePoint offers a rather simple solution of creating a custom help in a site collection scope, which is a more standard solution. The key is to activate the
Custom Site Collection Help site collection feature. Further reading at support.office.com.
Why not to create a custom solution for this? Sure it's possible in a way or another. You, however, should need to consider at least the (automatic) help page creation, a possible blank help page, how it would replace the OOTB help-button and possible search issues with similar looking pages based on title/content.