What is average price for 3D parabola?
The price dependss roughly on material, machine hours, operator labour, profit and administrative overhead.
Some companies deduce the operator labour, machine hours and overhead to roughly 10 times the material cost. I think that is kind of fair. In your case I assume that you use PLA, the perabola is hollow (just a flat surface) and the company needs to construct the 3D model the parabola to a specific tolerance.
this model in PLA should not cost more than \$5 in filament, so about $ 50 should be an okay price for your parabola. The total price of \$147 leaves about \$97 for modeling the parabola. I think that's fair, given that a non-mathician has to find a way to construct a model and test the results.
If, for example, you want a metal print and you provide the 3D model I find the price of \$147 to be very normal. These metal printers are very expensive, labour intensive and eat up energy.
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All above is just my best guess, given the data you provided. Expect a better answer when you provide more data.