I am long retired (2008) In the field of cardiology I am a pariah, there is an embargo on my publishing in major journals. I have therefore been forced to go to obscure journals where the referees are not from the cartel that ban me. J Cardiol Cardiovasc Med. and J. Integr. Cardiol. I have so far with these journals persuaded them to accept only cost covering fees, i.e. reduced from over £2000 to around £500. It is embarrassing to do this and with 5 papers already done this way in last 2-3 years hurts my measly pension. I now have a sixth to submit and it is again ground breaking and against the establishment's dogma, the reason for the embargo. I have tried various funding agencies but there are none I can find to get funding of anysort, e.g. I need an updated Mac.
The Directory of Open Access Journals (DOAJ) currently lists 1,845 open access journals in the field of Medicine that do not charge any publication fees.
You could use the advanced query functions to the left to narrow down your discipline (e.g. to Internal Medicine), and browse through the list of journals to find some that may be suitable to you. That way you would not need any funding at all.
Suggestion 1: I notice you've spent most of your career at the University of Cambridge. Are you a member of the Cambridge Philosophical Society? Providing financial support to a member in this situation sounds like the sort of thing they might consider to be within their remit (assuming that they don't know of some good reason why you really should be a pariah).
Suggestion 2: I believe you first expressed the view that a cartel of referees was rejecting your papers from mainstream journals for scientifically unsound reasons c. 2007. Even assuming that you were completely right about that at the time, are you sure the cartel is still operating after all these years?