Open Access will save on more than just journal subscription costs.
"[...] as more and more scholarly content becomes available online and open access, the need for academic library acquisitions departments will decrease dramatically.
This change will have an added benefit for libraries, for in addition to saving money on subscription costs, they will also reap savings from no longer having to bear the salary costs of those involved in collection development, ordering, and licensing library materials.
In most academic libraries, collection development and acquisitions departments are still organized in much the same way they were in the print era."
Via Pavlinka Kovatcheva