According to my casual Googling, metal lathes start out a lot more expensive than 3d printers. Wood lathes and CNC machines are surprisingly affordable though. So this seems like a good question.
Not only that, but if you consider a cheap second hand lathe mostly as a source of parts and rebuild the frame out of something like synthetic granite (which is mostly a casting job) then it'll probably have much better rigidity than anything you can buy at a similar price.
