What should I charge for cabinet doors in MDF finished with Ilva paint?

I've gotten an inquiry about making milled cabinet doors in MDF, which will be sold commercially, finished with a water-based semi-sheen paint but I don't know how to price it out. Should I charge by square foot? Linear feet? Per cabinet? And how much? What do you charge for the woodwork vs. paint? They have also requested some volume discount, and I don't know how to price it out.