It looks like there are about 55 people listed as reporters, correspondents, moderators listed on the site. I do not know how many are actively contributing. I believe in the past there was a yearly, honorary, stipend of about $500 per person who contributed. About 10 years ago a leader of ProMed told me that it cost 75K a year to operate.
The cost breakdown of 1.5 million USD would be very interesting to see. Who are the large donors that have been supporting the 1.5 million USD budget?