First, there's cost of materials or cost of goods sold. Second, there is labor cost. Third, there is a "premium" cost because you are unique.

Materials cost is easy. Add up the cost of everything you use to make a photo and divide by the number of units sold:
Regular B/W photo paper costs between \$1 and \$2 per sheet.
Regular B/W film costs between \$2 and \$5 per roll.
Chemistry for film costs around \$2 per roll. Chemistry for paper costs from \$2 to \$5 per batch.
These numbers vary depending on what you buy, the brands you choose, whether you buy in bulk or at a discount. These numbers come off the top of my head. Just crude examples. Your figures will be different.

Don't forget to throw in a few extra bucks for the cost of wear and tear on your equipment. You have to buy cameras, enlargers, film tanks, print developing trays, thermometers, utensils, lab ware and other consumables just to get started in your darkroom. Don't charge too much but don't be afraid to add a buck or two to your cost to account for it. I just round my numbers up to cover this cost.

Let's imagine you shot two rolls of film and made ten 8x10 prints out of the batch:
Film and processing might cost you \$10. Printing might cost you \$20. Total cost = \$30.
(Again, just examples off the top of my head. You'll have to do your own math.)

So, next what's your labor cost?
How much do you get paid for your work? I can easily get paid \$15 per hour.
Whether you spend your time working in the darkroom versus going to your regular job makes no difference. That's the minimum amount your time is worth. Maybe your time is worth more.

Add up your time in the field or in the studio. (2 hours?)
Total = 7.5 hours. (Round up to 8.)

8 hrs. * \$15/hr = \$120

Right there's the minimum amount you need to charge to break even. If you charge less than \$120 you're losing money.

Other things to consider: Automobile: Did you drive to the location? How much does gas cost? Envelopes, folders or postage: Add in for that.
What about other miscellaneous items? Pencils, paperclips, gaff tape? Who knows what? Add them in.

We're probably up to somewhere between \$125 and \$150, now. Aren't we?

Next, we have to tackle the subject of premium cost. This is tricky.
Just ask yourself, "What am I worth?" and "What is it worth for somebody to hold a handmade, traditional photograph in their hands?"

Are you well known enough or is your art evocative enough to demand a premium?
Ansel Adams could demand a large amount just for the privilege of owning one of his photos. Joe Schmoe, down the street, virtually unknown, probably couldn't demand anything?
You're somewhere in between, I'm guessing.

Then, finally, when you have your price, don't forget to consider the old "Friends and Family Discount."
If you know the person, if you think they are nice, if they are close friends or family, if they might refer you new clients, go ahead and knock a few bucks off the price. (10% or 20%)
If you do give a Friends and Family Discount, tell them about it and tell them how much.

1 to 2 hours photographing. 2 rolls of film. Lab time. Darkroom time. Prints. Finishing time. Delivery or Postage. Extras or incidentals.
\$125 to \$150. Round up for your premium if you can demand it. Let's say your total price is \$150 to \$200 for the package.

Friends and family discount, if you decide to apply it, might bring you down to somewhere in the \$175 area.