My brother used to cast resin pen blanks in the garage. It's a pretty simple process that just needs a few silicone molds, a pressure vessel, and a vacuum pump. He sold them wholesale to a woodworking supply place for $5-10 each. He made enough over a couple years to pay for college.
I know a few people that must make good money resin-casting RPG dice. Some are super-fancy with all kinds of embedded decorations but one is just a clone of original D&D Basic Set dice (aka "Holmes dice"). Can't keep them in stock.
