Based on data supplied by Mark Ware in the recently released STM report, An Overview of Scientific and Scholarly Journal Publishing, my calculation is that a full flip from subscriptions to full OA via article processing fees at the PLoS One rate of $1,350, would be 64% - about two-thirds.
In brief, dividing the $8 billion annual STM revenue as reported by Ware with the 1.5 million total article production per year, we arrive at a total of $5,333 average STM revenue per scholarly article produced (that's ALL articles, not just STM articles). Compare this with the PLoS One rate of $1,350 per article! PLoS One is four times as affordable.
Factoring in Ware's report that the library share of this revenue is about 70%, we get savings of 64%, or two thirds. At the slightly higher BMC standard APF rate of $1,535, library savings would still be 60%.
There are many limitations to this brief study. It is important to note that the majority of OA journals do NOT charge article processing fees. This data is provided just as an illustration of how cost- effective open access can be.
Most of the limitations of this study tend to underestimate cost savings for libraries with a flip to OA. For example, non-STM revenue is not taken into account; assuming more than $8 billion in revenue now, the cost savings for libraries would increase. Also, non-library sources for article processing fees, such as authors able to tap into research funding grants, is not taken into account.
This is not to say that libraries can afford just any article processing fees. While there are still savings at an average of $3,000 per article as some publishers charge, the two-thirds savings depends on supporting affordable publishers.
For more details and links to figures: http://poeticeconomics.blogspot.com/2009/10/research-brief-library-savings-from.html Happy Open Access Week! Heather Morrison, MLIS The Imaginary Journal of Poetic Economics http://poeticeconomics.blogspot.com