There are many newspapers that do not have as much money as the New York Times or Washington post, and many of them struggle with tight margins.
It also seems likely that there would be other costs than the salary of a public editor: typically they would have a column which costs space on paper and the results of the editor’s opinions on ethics could increase other costs for the paper (higher standards, more discarded stories, being slower to print because of higher standards, possibly higher employee turnover or hiring difficulties or exposure to lawsuits)
Forget the rest, the NYTimes and the WaPo can certainly afford a team of public editors, if nothing else but for the long-term credibility of their own institutions, never mind the side benefit of keeping them honest.
It also seems likely that there would be other costs than the salary of a public editor: typically they would have a column which costs space on paper and the results of the editor’s opinions on ethics could increase other costs for the paper (higher standards, more discarded stories, being slower to print because of higher standards, possibly higher employee turnover or hiring difficulties or exposure to lawsuits)