Hi @ihlasnobatovich
This might be a long story, but the gist of doi registration is no more different than domain registration. Although, some companies state that they are non-profit, it just makes me smile. It’s a market of millions of dollars. Anyone wishing to get this service has to sign an agreement with a doi registration agency and pay an annuel fee, which is at least 275 dollars. For each article, you have to pay 1 dollar, even for an update. The access policy of your journal has no effect on this. Long story short, the only free and quality service that you might get on this road is the Open Journal Software and this forum. A big thanks to developers and contributors.
Please look at that topic too.
https://forum.pkp.sfu.ca/t/crossref-vs-datacite/35148
Regards.