My wife and I made a google document that allows you to import measurements in volume. The document then converts that into how much it cost per plant. We give this to our patients that we added so they can see a visual of where their money is going.
But the trick is converting everything over to a volume. Ie. Measure a tablespoon of soil then weigh it.


For cost of equipment we totaled up everything than divided by 365.5 to get a payment cost that is by day.

Have to fire up and old mac to get that document but I can post it if you want.