This is pretty interesting, lets do the math:
$15.99 online retail
Ecomm sites need at least 40% margins on advertised prices. This is just to keep the lights on, open the doors, pay employees, warehouse space, etc. Let alone the loss on free shipping.
So, whole sale is max ~$11....retailer profit at $4-$5
Well, the manufacturer Rossi, assuming Rossi contracted it out, needs to make at least 50% to pay the bills.
Landed cost at Rossi ~$6ish. $4.00-$5 profit per unit, assuming retailer pays freight. Not including dealer discounts, most large retailers get 10% off wholesale. MOQ minimum at 1000 pieces
(*very different from Weaver, who orders in 5000+ increments. and has multiple base(s) that fit multiple rifles, as in their 2 piece sets)
Current cost of aluminum, milling, screw cost, packaging, freight from China, +DUTY, sounds about right. Might be a little wiggle room for contracted importation.
So, if someone here wanted to make this same item in China... Assuming you have the factory contacts, a sample to send the factory (or engineering drawings of the base), can fork out the $3000 to build them to hit the MOQ, more money for shipping (probably $300ish?), and do all the legal documents thru customs, pay for packaging. You now can sell them to a retailer at wholesale prices or try to sell direct thru a website, then you need to build an ecomm platform. You can certainly do this in the 120 days it takes to build and receive the bases.
All in all, if you are to make and market this yourself at a competitive retail, you may see $4 per unit in profit if you get it into a large retailer. Could always sell direct and price gouge to increase profits, but from my experience, 75% of people will wait on back order for the better priced item. Then you have to worry about warranty issues, legal claims if the base fails, returns, QC checks for tolerance, etc.
I know that is a somewhat lengthy synopsis, but it shows somewhat of what goes into manufacturing an item off shore. To manufacture here? Just what your time is worth, I don't mill, but I'm guessing aluminum prices here are higher and you would want a computerized cnc machine to get the exact tolerances and then you can pump them out. Still need to check, finish, and package them. Be very interesting to see what it would cost for someone with a mill to make, finished with screws.
Its a lot of time and work into $4000-$5000 in potential profits that you wont see for at least 150 days after initial investment, and not including payment for time and office like services, or taxes paid. (if you go the import route). This is why the big mount companies only pick up what is proven to make profits.
Who you should email is EGW. They are great at making mounts quick and watch what the demand is for.