Ok, I have to start right off letting you know that this post will not reveal a formula for pricing your work! The fact is, there is no formula. Even though I've been creating commissioned mosaic for about 2 decades, I still don't have a solid equation for mosaic projects.
When I was just getting started, I remember being very confused about how to price my work. I just made up numbers by guessing how long it would take me and how much materials would cost, and I was working for peanuts. Honestly, that is how you start. If you are like me, you are getting started with very basic skills and each project poses new and unanticipated challenges. You are making mistakes and learning as you go. Price accordingly and be honest with yourself. Do as many projects as possible in your own home or as favors for friends in order to learn and build your portfolio before accepting commissions. I can't stress enough how important this is! If you take on a corporate or public art project before you understand the properties of adhesives and how they combine with different substrates, you are setting yourself up for a disaster.
The above image is a glass-on-glass mosaic I made for a restaurant in Olympia, WA back in about 2008 as a privacy screen between the kitchen and dining area. The design is sweet, but I did not yet understand the concept of andamento and the lines are rudimentary. I made two of these, about 36" wide, for about $900 in food credit. Twelve years later, the work would be much more sophisticated and I would charge $3000 for the labor alone now. Unless the client asked me to reproduce this design (or provided a design) there would be a design fee. If I were expected to install the panels, that would be additional. Otherwise, there would be a delivery fee.
In the years between then and now, my per-square-foot fee has slowly increased in keeping with my skill level, experience and reputation. By now, my work is installed nationwide, my CV is extensive, I know what I'm doing, and I now carry business insurance, have a contractor's license, and I'm incorporated. These are considerations for your pricing structure.
My first step toward making this work into my business was to enroll in a 3-month-long business course offered by a great local organization that helps people start micro-businesses. By the time I completed the program, I had learned about marketing, taxes, liability, etc, and had a business plan approved by a financial advisor. A couple of years later, I took a "Business of Craft" weekend workshop that was more specific to creative commerce, and it gave me more tools to apply to my own business. In 2012, I took Laurel True's "Business of Mosaic" class, which was intense! I highly recommend her workshop, if you can take it. But honestly, even with all of this information, I still had to figure out my own pricing because my particular situation is unique to me. The work I make is different from other mosaic artists. My needs are different. My local market is specific, and I adjust accordingly. Each individual project has its own considerations; is it a simple design, or more complex? Is it flat or dimensional? Stylized and simple, or complex and representational? What are the materials and tools required? Can I work on it in my studio, or will I need to travel to the site? Will I be doing the installation? Or will I need to build crates and ship something heavy to another state? Will I need to rent scaffolding? A crane? Do I need to contract others to help with aspects of the work, like the stone carver who created the inlays in these boulders?
If you are making straightforward rectangular mosaic art that is either hung on a wall or installed in a backsplash (for instance) you can more easily come up with a square-foot or square-inch price. If that's the case, I recommend you do some research, looking at other artists' prices. Try to be objective about your work and compare yourself to others at the same level, and in a similar category style-wise. Try to match your market as well as you can. If you underprice your work, it hurts your colleagues. Many years ago when I still sold at festivals, my booth was placed right next to another mosaic artist, unfortunately. She made small, simple mosaic onto the glass in reclaimed picture frames she had bought secondhand, and she lived next door to a stained glass factory where she gleaned all of her glass for free. Her mosaics were all $25. Mine were $100-$500, much more elaborate and diverse, though also using reclaimed materials and bases. I didn't stand a chance. With sites like Etsy, this kind of thing is happening all the time.
So, it's tricky. You need to start somewhere. But you don't want to underprice your work. That is a balance each artist needs to find on their own. I've had people send me photos of their work, asking, "How much should I charge for this?" I cannot answer this question. I'm sorry, because I was once where you are and I know it's confusing. Each artist needs to figure out their market and their pricing, and in time, you'll find it.
If it helps, my range for fabrication is $200-$1200 per s.f. $200 is my simplest style, precision cutting or randomized patterning with relatively large pieces. $1200 would be intricate realism like portraits. Those are very hard and take forever. I now have price lists for materials, and that is a separate line item. Smalti runs about $80/s.f.. Stone is about $40/s.f. Stained glass is a wide range, depending on type. Cool colors of glass cost less than warm colors due to the minerals used. There is a design fee, sometimes admin fee for the hours spent working out details. I usually install my own projects and I charge a daily rate for that. Now, with public art, there is always a set budget. In those cases, I have to work backward, estimating the cost of each part of the process, and letting that define the scope of the project.
So, in sum, there is just no easy answer to the question about pricing your work. But I hope this gives you some things to think about. Be sure to track your time on projects, especially at first. This will help you a lot. If it takes two days to complete a square foot, consider that in your labor cost. But maybe you are able to complete a square foot in two hours? This will help you determine your rate.
I hope this is helpful! Thanks for reading and have fun making mosaic!