What I am doing so far is to walk through the steps involved and estimate what I think is reasonable, factor in costs that are large such as the bulk of the materials and consumables. I allow a $45 hour shop rate. then I double that. so I also call around and am constantly shopping prices wherever I see something similar. How much you get for an Item depends more on how you present it rather how well you make it. I make stuff that is vastly better than the crap I see sold all over but nobody knows about me. Also in many cases it doesn't matter whether the quality is there, if it is too high it is too high, cheapen the design and quality like Walmart, shudder, or find clients with deeper pockets.
Ain't nothing to this stuff. ;)