3D printed guns are very reliable, can last many rounds, and require zero skills beyond the means to source a good 3D printer and find the program files.
The printed block does require some trimming etc, depending on your desire for aesthetics I suppose.
Certain parts must still be made of metal, obviously, such as (preferably) the barrel, firing pin, etc but most of those can be purchased online without triggering the attention of the authorities. I don’t think they’re cheaper than purchasing an actual weapon, but I also don’t think that’s the point - they avoid the scrutiny and investigations that the purchase of a legal gun would generate.
They used to be 100% legal, as they filled a loophole that the US gun laws failed to anticipate (who knew). However, they are know banned in most of the US as far as I know and certainly in NJ; possession of the weapon is criminalized as is the creation of them.