One very basic one that I see is "how much employee time am I saving you?"
If a company pays its engineers $75/hour, saving 10 hours of engineer time is worth $750/month!
That's a high number -- plus, it's on you to prove you really can save that much time with your service -- but I think it's a reasonable starting point.
As a consumer I like subscriptions because I can easily calculate, “how much time and effort do I spend doing X, is it worth $_____ a month for that?”
My career has been enterprise software for internal apps so I’ve never sold software before. Setting costs feels like a WAG (at least initially).