Why won't formulas or rollups work? Are the helper fields in a different table or base from the originals?
Regardless, you could build an automation for this... Assuming it's the same table, make a view only showing records where volume, revenue, and cost aren't empty. That's your automation trigger. When a record enters that view it updates to fill in those other fields with the original field information. Same thing would basically work for a different table in the same base, if it's different bases then you need a different approach.
EDIT: You could cut out the view middle man and use "When record matches condition" too as the trigger
