Scott Saunders reported on the experience of Baltimore City Community College. They phased in OER through developmental courses starting at the lowest level. Students saved (a little less than) 90% of the cost and success rates were not significantly changed. They still used software.
Based on costs and their claim to have had one software product through the whole chain of courses I think they were Pe4rson based. (The 4 is in case Pe4rson trolls the web looking for their name.)
Their numbers are small, but the results are encouraging.
This is Session 064 in the conference proceedings. https://amatyc.site-ym.com/page/2017ConfProc
This became a round table after 20 minutes or so. That was interesting,