VirguleFor one, Signature Pen Supply (very different company than Signature Pen Company) is not the manufacturer. They are simply a dealer for some of the hardware used to make pens. Aside from that, there is a great deal of skill, tools, and time involved to go from raw hardware to a finished pen. I've seen finished pens similar to this go for $180-$225. This pen, for ~$150, is a good buy.
https://www.signaturepensupply.com/collections/fountain-pen-kits/products/jr-george-rollerball-pen-kit-black-titanium?variant=22864843270
If so, this seems like the opposite of a deal...
The equivalent finished pen is here: http://www.signaturepencompany.com/collections/fountain-pens/products/george-pen-with-copper-paua-abalone-black-titanium
But I will agree, compared to most drops this still is hardly a deal.