> "So in the 70s you could pay per request billed to millisecond precision?"

It's been a while since I encountered it but yes, mainframe time was so blisteringly expensive that usage was accounted for on a per-job basis and billed to individual user accounts. I don't recall the resolution or pricing anymore but students would be issued an hour or so (?) of processing time to complete their coursework per semester. Perhaps somebody with better recall than I can fill in the details.