Jyrki Ilva et al. have published "The Costs of Open and Closed Access: Using the Finnish Research Output as an Example" in LIBER Quarterly.
Here's an excerpt:
As business models of Open Access publishing are still under development, the aim of our paper is to assess the statistical tools and data that the Finnish libraries currently have for comparing the costs associated with different modes of disseminating scientific publications. We will also analyse the potential costs associated with Open Access publishing models and compare them with the current cost structure of—mostly—paywalled (PW) access. . . . We will discuss the alternatives on how best to develop statistical tools to estimate the true costs of scientific publishing.