Certainly not a sigma. There is one 40mm that I am lusting about, but the lens itself is 1200 USD and would have to be used via adapter, so no native performance with stopping the aperture down, etc – it's a Skopagon 40/2. Distagon type of design, my dream lens, but it's a DKL mount. I know there are adapters from DKL to Nikon, but I reckon you can't set the lens to f4, meter wide open and then have the camera stop it down via adapter. If that was possible I would definitely go for the FM3A.
I found an FM3A on facebook marketplace, pristine condition, bundled with a 1.2 fifty, for 500 bucks. Seems like an amazing deal, talking to seller now.