I have been doing 3D printing and design services for over three years. I do most of my design work in FreeCAD with some use of Blender and Meshmixer. I have wrote several FreeCAD 3D Printing 4 Kids! ebooks. Besides designs for FDM printers, I can also design for services like Shapeways and am very aware of issues like wall thickness. I charge a $10 setup fee plus $ 0.20 per gram (not by volume, which allows some savings since I allow you to set the infill). I am Pierrimus on Thingiverse and Pinshape. I charge $25/hr for design services.