you might also want to look at openscad.
Not only could you simply input the equations and have it generate a 3d graph, but you can import 2d dxf files and extrude them into 3d very easily.
And it's free software :-)
Ralph's suggestions are anything but free ;-)

If you're graphing program won't export as dxf - simply use a screen grab and convert it in a paint program.

Haven't looked at cura for a while, but sure I remember it had an extrude option for jpegs or png files. There are add on modules, sure one was an extrude function.