Additive, Substitutive, Subtractive - The Scholarly Kitchen

"We do have a number of divergent figures, however, that are likely to be reconciled in some way in the years ahead; these are in fact the two metrics that I personally keep an eye on. The first is that the average income to the publisher per article is about $5,000. You derive this number with great mathematical sophistication, by dividing the number of articles published each year (about 2 million) into the size of the journals market (about $10 billion). Voila! We now have a benchmark against we can measure OA pricing and services."