> The impression I got was that there are no paid core developers for PostgreSQL, is that correct?
There are (I and several of my colleagues, for example) - but they're paid by employers having us work on postgres, rather than a foundation or such.
> If so, what's the best way to support the project financially?
There unfortunately - personal opinion, not as a core team member - is no good way to fund a "partial" developer for postgres right now.
On a smaller scale than employing a dedicated postgres developer, regularly testing the in-development release (and reporting bugs!), doing ad-hoc testing, patch review etc are a bit easier to start with.