There are always two sides to the cost of something. It doesn’t matter if it is a watch, a car, or a hair brush. How much does it cost to produce it, and what is the value to the person purchasing it.
Any time it appears the sale price is well above the cost of manufacturing, someone else will jump in and start manufacturing as well. This drives the selling price down. If enough people jump in, the selling price may drop below the amount at which it is profitable to produce and sell the item. This causes some to leave the market, which will let the selling price rise again. Usually, and particularly for commodities an equilibrium selling price will emerge. This results in our having a general notion of what a generic watch, car, or hair brush is sold for, or worth. Of course there will be a diamond encrusted version of each, which will rightly or wrongly be valued much higher than the generic version.
With photos, there is the notion of value. If you photograph my Aunt Mary, and produce a print, your photo may end up on her wall above the fireplace. The value will be that friends and relatives can admire her likeness during the parties she throws. The sale price will have to fit into her budget and she will have to value your work enough to pay your price. If you photograph Miss Recently, and she is going to use the photo with her byline in newspapers and magazines distributed to hundreds of thousands, daily, or weekly, then the value to Miss Recently may be much higher than it was to Aunt Mary. Or not. Who knows. Though if she is willing to pay $150 as a sitting fee, it suggests she values your work more than what it would cost her to get her cell phone from her purse and shoot a selfie.
Your challenge is to figure out how much value Miss Recently places on having a quality photo to include with her articles. Too high a number and you may lose the sale. Too low a number and you are leaving money on the table.
A business tutor I was speaking with last year had a similar photo taken by one of his students. It cost him $250 for the sitting fee and the digital file was thrown in. He thought he got a really good deal. I think the photo went on his web page. I have heard of other photographers who have tried to gauge circulation of the photo and charged a few cents per copy.
Once you have covered all your costs, the rest is profit. How much profit there is depends on your negotiating skills and how much distance you can put between your photo as a commodity and your photo as a unique work of art.