Find your true costs to produce the job, then find the market sell price for the same work, what customers are actually paying.
There is no point in doing the job if you will lose money on it because it costs more to produce than you can sell it for.
Stephen Marsh
One of the more difficult things to do, though, is to determine your "true costs".
There are formulas, but they are based on some "difficult to determine" assumptions: how much a month do you expect to pay for labour, shop rental, machine rental, your own pay, supplies, etc. Divide that total by the amount of production units (for example, "clicks") you expect to make in a month and you have a very rough idea of your costs per production unit.
The problems, though, are that you must allow for spoilage and stupidity among other things. There will be times when you will have electrical failures, etc.
And this tells you something only about your
costs. It tells you nothing about what you can or should charge to the customer (the "price").
The only reasonable way to figure prices is to see what your customers are willing to pay. There is no real formula for pricing... because if there
were a formula, someone would cut below the "formula price" to be competitive and capture the work. That's the nature of competitive marketplace capitalism.
Some items will require very low margins (the difference between cost and price) and some items will allow very high margins. Most items produced by a small shop will bear a 30% markup, a slightly smaller number a 40% markup, and a very few a 100% markup... but this tells you nothing, really. You could always mark up 25% and get almost any job you bid on... and go broke. I assume that going broke is not your plan.
The margin can often be very different on exactly the same product being sold in a different context. (Over the years I have seen things like business cards, costing about $15 wholesale, being sold for under cost at $13 and for as much as $250... in very different sales contexts. Both were "fair prices" at the time, at least as far as I see it and as far as the customer saw it at the time of purchasing.)
So it comes back to what Stephen said: "Find the market sell price"... and then twist and turn and run and jump and do whatever it takes to make money at that price... or don't sell that item except as a "loss leader".
I'm sorry that the answer to your question is that "there is no easy answer"... but that is the plain, unvarnished truth.
Otherwise my employer would have replaced me years ago and saved a lot of money.