Wikipedia says prototype runs are done MPW or MLM, with many different chips printed on a single wafer. Nobody quotes actual prices, of course, so guess "a lot"

Wikipedia says prototype runs are done MPW or MLM, with many different chips printed on a single wafer. Nobody quotes actual prices, of course, so guess "a lot" https://en.wikipedia.org/wiki/Multi-project_wafer_service https://en.wikipedia.org/wiki/Multi-project_wafer_service