What is a good price for an adventure?
I asked myself what I want to make if I sold a hundred copies? Generally the answer is $500. Now this not list price but after OBS takes it cut. So I peg it a roughly $5 per copy. Which on DriveThru means I need to sell the PDF for around $7.99. The print cost is higher depending on format but I make it work so I am clearing around $5 per copy print or PDF.
But there is a catch for me. I have to feel that it is worth $7.99 to the reader. So I generally will make it 64 pages to 96 pages by adding a supplement to the back half of the adventure. It not needed to run the adventure but it is related and it is there to make the product useful beyond it use as an adventure. Basically use my skill with small setting, like Blackmarsh, to make something useful with the adventure one thing you could do within that small setting. Also the two halves are distinctly formatted.
If I was to write only an adventure then I would go for $300 for 100 copies. Which means I can sell the PDF for around $4.99. Again print is higher because of the added print cost. However keep in mind the amount of work as a DiY publisher isn't that much more. And may make the product more useful if it doesn't clutter up the adventure. Which can be done by making the work into two distinct but related halves.
So generally my observation is that people found going through the publishing worthwhile if they gain 100 sales over a year. The point is not the money, although it useful, but more it is a useful barometer of folks approval. Sustained sales over a year means people are found your stuff useful.
So what about free? I give away stuff for free all the time. And even have the PDF for one of my major works, Blackmarsh, free. However all the free stuff is what I consider to be an effective form of advertising. The stuff that I pay or barter for edits, layouts, and art. I will sell. Although I am at the point where my publishing now funds my hobby. The main reason I charge so I can pay for more art, and more editing. The two areas I am weak on. Except for Blackmarsh all the free stuff are first and second draft with basic layout done with Word and self-edited.
Don't sell yourself short. Especially if you are willing to learn both creatively and the logistics of publishing. Figure out a per copy profit that allows you to do the next project a bit better and give you and your significant other a dinner or you that RPG books you wanted for a while. If you can get a 100 sales over a year, it will be worth it.