Part of the reason that Postgres is popular is that there are multiple companies selling support for it, several of which are also major contributors. So there's actual competition to keep prices somewhat under control.
I disagree that there's PostgreSQL support out there. When I was having serious performance issues, I did a ton of Googling and couldn't find a single place that could offer a-la-carte support, only very, very expensive yearly subscriptions from questionable places - ie. no name brand consultants or anyone connected to PostgreSQL itself.