(1) Do you account for your hobby project time spend/investment? (2) Do you “bill” for the time or have a way of measuring the cost? Or, (3) do you measure the amortized cost?
The proper way to understand is this. You can measure the cost of everything in terms of real resources such as labor, time, energy, materials, etc. But generally, the actual cost is unknown due to undetermined variables about how long particular tools last, and therefore, waht is their corresponding cost share over the length of their service life.
Also, there are market value dynamics: You can’t do anything “for free” without also implicitly influencing the market value. But, remember this. Price is determined by market value. At very minimum, market value is determined by two parties: the seller and the buyer.
Funny thing I realized: In practice, personal electronics hobby projects do in fact have a “market.” When you bust out your electronics tools, you take on a different personality versus when they are stowed away. So, in essence, one person is providing a good/service to another person, though in reality, these are merely different personalities, or workflows, of a single person.
The point is this. The buyer wants to be able to account for all involved costs, their primary hope being to instill some sense of reliability for the future. Namely, can this same product be reordered in the future, and at what cost? This is true regardless of who is paying for the individual costs, and regardless of what the cost to themself is.
Then, you can look at the actual cost/payment breakdown and determine where there is likely to be the greatest variability in costs. That is, when conditions are most likely to change, and how that will have an effect on the costs. Usually, for custom bespoke jobs, the effect is to increase the cost for a second time through, simply because matching custom resources are no longer as cheap and abundant as they previously were when the project was performed years ago. For example, the fact that you may have been able to get one service “for free” in the past, but now you have to pay someone else to get it in the future. So you can look at that, and determine what the cost should be based off of expected market values for similar services that are more available from a more massive market.