They rent or own a building that houses their operation, pay mortgages or rent, stock inventory, advertise, mark up merchandise, hire sales personnel and deal with walk-in customers. Glance through the trade directories and make a list of national and regional magazines, their editor names and their telephone number or address. Then start the sales pitch. They're all listed in Writer's Market. You can also request that the magazine cover supplies and developing costs.
Every dollar adds up.
I'd offer only black and white unless the editor insists on color. Your best photos will be exterior shots where the subjects need no additional lighting. That way you don't have to deal with f-stops, flashes, etc. Have the owner stand in front of the shop window or door. For black and white, shoot one, 24-exposure roll per interview and have the developers print you out a proof sheet.