This is what I do. It's who I am. I tried other, smarter, better, things. Turns out this is me. It isn't like I have a lot of choice. Life would be easier if I did.
i have to do something similar to that when i "price out a job".
figure out how much your materials cost per image
( film chemistry and paper ) and how much time it takes to make an image.
figure out how much you want to make " per hour" multiply that by the time it takes to make a print ( shooting and printing ).
compare your lab-fee to an expensive lab that does commercial work.
( or use the lab as your printing costs and add your hourly fee for shooting on top of that ).