Well, I was also thinking the same. The 3D printers are so expensive right now, but one day maybe everyone would be able to afford it just like 2D printers.
Wait.. can't I just 3D-print a 3D printer?
Technically you can, you'll need many 3D printers that are specialized in different parts to make the whole 3D printer
why? because a 3D printer, is composed of mechanical parts, electronic parts, electromagnetic parts in some cases (lasers and what's not) .............
Today there isn't a single printers that does everything, there are 3d printer that can make most of the mechanical parts but from there you'll need the rest of the parts
and you'll need to put them together by yourself