If so, are you willing to quote a price per cubic inch of material (I would say 2-3x the material cost would be fair)? Or are you willing to quote once an STL is supplied?
I would say the best way it so quote by time. Around $35 per hour would be fair.
is to…damn keyboard lol 
Depending on the size of the project I’d be willing to look at an STL and give a quote on it. Shoot me an email at dyjax@expensivehabitengineering.com and we can discuss it more.