Fascinating conversation. Not sure what the original point of this thread was - how to price product, or how to check profitability? I worked for one of the sign franchises at a corporate owned store many years ago. We always had a basic rule that helped frame cost of a product: 25% material costs, 25% labor, 25% overhead (rent, electricity, equipment), and 25% profit. On things purchased for resale, markup standard is 40%.
Another thing is often overlooked is turns. So big businesses can run on a lower profit margin by utilizing turns - which is how frequently you can take your investment in materials and sell as product and then do it again. For example, if I price a skid of coroplast such that I make 40% profit on each sign, but it takes me 8 weeks to sell that many signs I can make a 40% on goods sold. But if I can price such that I make 10% profit and sell a skid a week, over 8 weeks I have taken that same original investment in materials and "turned" it over 8 times - thus making an 80% profit, or twice the profit of pricing at 40%.
Now for most of sign shops, increasing volume has more to do with marketing and quality than price. At a large scale, and for large projects, price becomes a large factor. I feel strongly that one should consider the total investment in materials and look at the amount of time that investment will to turn back into cash for profit and re-investment into materials for the next project. Big customers often want 30 or 60 days to pay after completion, while most suppliers want to paid within 30 days. Small customers often pay at completion, so small investments can turn around quickly. A company that prints coroplast for you, like Firesprint, does so quickly, so even focusing on high volume, turns can be relatively fast but not as fast as lettering Joe the Plumber's van.
Looking at another business type, both my father and great uncle were plumbers. Uncle Arthur told my dad that he was successful because he focused on domestic repairs - payment at the completion of job and low risk of lack of payment. Dad had a lot of builders courting him - long times between payments, more invested and at risk. Some builders go under and you have to fight to get your material costs back. But when it runs smoothly, you get large volumes of work.
My point is big volume can mean big profits on a low margin, but risks are higher. Small volumes jobs can have high profit margins and more turns with lower risk.
Just a bit of food for thought.