Learning how to create 3D models on a computer might be a good place to start, and won’t cost you anything to get started. Download Blender and do a Google search for tutorials. Make some sketches on paper and see if you can’t re-create them in the program. 3D printers are becoming cheaper every-day, so that might be worth looking into as well. Of course there’s always design/engineering classes in college, although you could probably find good ones on iTunes U for free.