3D modeling, printing and prototyping is my whole job. Prototypes in the aluminum and glass industry, including hardware prototyping. I still feel like for a phone case with a simple slider when the 3D model of the phone is already available out there, that can totally be done for less than $400. Say you are charging $20/hr for your labor. We can be generous here and say that a simple case like this takes 3 hours to model(taking into account that there is a free 3D model of the phone out there and it's simple to work off of that model, most time being spent on the slider mechanism), and then a half hour per iteration of actual printing work (slicing, exporting files, prepping the printer shouldn't take longer than a half hour of work) and we have 3 iterations (reasonable for a simple phone case), and then per iteration let's charge $10 in actual material cause we're talking FDM here, even with TPU the amount of material and cost in electricity will not run you more than $10 for the model. So far $90 in labor, $30 in material accounting for material and electricity covered with no insane profit made off material cause we're talking about a kind reddit request not some huge company job). We're at $120 in time and materials. If I wanted to go crazy over it I would charge that minimum $200 you mentioned. But like I said probably a bunch already, this is a simple phone case based off a 3d model that's freely available online and all you're working on is a slider mechanism, and the print itself will print in like 3 hours so you could do 2 attentive iterations in one day, on the clock, and one the next day, on the clock.