Not even amd/nvidia have their own fab at this point so it is probably safe to say you wouldn't need one for that either. You'd still need tons of cash of course but not quite as much.
The existing fabs (TSMC, Samsung, GF etc and possibly even Intel under their new strategy) would probably make the chips you designed, if you pay for enough volume that is.
And who would make the tens of billions of investment to build a fab for that?