One of the objectives of the Safeguarding the Nation's Digital Memory project which produced DiAGRAM was to help archivists (in particular) make the case for digital preservation work. Part of this is having a built in benchmark model to help demonstrate the difference between merely backing-up material and actually doing digital preservation. If you’ve not explored the model yet, you can find the current (prototype) version at https://nationalarchives.shinyapps.io/DiAGRAM/
I’m happy to advise on using the modelling to help you make a business case.