You have to pay a designer to design them, first of all. If you make 10,000 grips with the design that person's cost ends up being very small for each set of grips. But its a completely different story if you only make 500. Then there is the machine setup cost, the test runs, etc. All these things add up quickly to the unit price, especially when you end up only making 500 of them after its all said and done.
So no, your $20 estimate is not realistic.
You have to pay a project manager too for the whole thing. That adds up as well.
Look, maybe Ruger is making just a bit more on these than their regular 1911s. Maybe.
But don't expect companies to come up with new, exclusive, limited-run products to just break even on their expenses for the project. And if they evaluate that they can add on $100 for the foundation and still sell it at a price point where they are guaranteed to sell them all, then thats another sound business decision.