Legally speaking, you can't receive payment for cannabis/marijuana product unless you're a dispensary. BUT. As a caregiver, I would suggest to charge a flat monthly fee to your patients for the labor of cultivation itself and the supplies you need, and ration their supply as needed. I was considering becoming a caregiver and floated the idea that I could basically bill for all the flower that their designated plant yielded and cycle it so you have 2-3 plants finish flowering/drying every 2-4 weeks for a regular supply. You have to talk to your patient though - do they use 1g/day and need 30g/month? Do they use 3g daily and need 90g/month? I would supply your patient with the amount that they need every 30 days, and bill them for the month.
Your supply cost is going to remain pretty much the same as you grow, and ultimately that is the only thing you can legally have your patients pay for.
