There are two 'difficult' parts to this. The first is the obtention of a file that a 3D printer can work with. Scanning can be done, with the right equipment, but there are those able to create darned good files 'from scratch', with enough experience in 3D modelling. Once one has the file, the next issue would be the material. Most domestic, hobby, printers use PLA filament, which is a very inexpensive plastic 'wire'. It's easy and cheap to work with, but does not have the mechanical qualities for all uses. Other filaments exist (notably ABS or nylon, but many more...), some of which can only be used by professional printers, often costing... well, even more than that..! For the RC 'planes I build, the parts I print (dummy motors, pilots, accessories...) have no other needs except to receive acrylic paint well, but for moving parts subject to wear, a more robust solution would be to get a quote from a 3D firm. The Yellow Pages would be a good start, or a web search. The economy of this depends on the importance, really. When PPE visors were required, they were cheap to do. A gear wheel could be pennies, could be pounds, depending on specification.
Hope this helps.