Visual DocBook editors

Dear All,

originally I've been searching for any free / low cost visual docbook editor
for rare use by various non-techie people within company as full-featured
product (e.g. Oxygen Author) seems to be an overkill. Unfortunately, there
are just several alternatives, none of them below $50. 

Sadly, DocBook doesn't seem to be offered as online tool for
interactive/collaborative editing in the cloud either. 

For e.g. LaTeX there are nice apps:
https://www.overleaf.com/
https://www.authorea.com/
https://www.sharelatex.com/

Have I overlooked any handy tool or service?

Please share.

Thanks, Jan