Additional Field to Folders

I would like to be able to list Purchase Price as well as Purchase Store under Folders. I can’t locate where I can add Purchase Price.

Purchase Store is already available as a folder field.

Can you elaborate on your suggestion to add Purchase Price? How would that work exactly a folder field? I mean, would that not create an enormous amount of separate folders?

I should have said “in addition to Purchase Store”, which I do use already. Since folders work the way they do I don’t suppose there is any way to have this as a calculation field for a range of entries? Maybe I’m straying into spreadsheet territory here.