For it to really be profitable, you need to have cheap laborers do it for you, like in Thailand. If it cost even 1k materials for a glass hull, 7k sale price that's 6k profit. Sell it for 4k, that's 3k profit and sell X amount more.
Yamaha SMC is the injection molding of composites, but glass hulls are more manual for inserts and bulk head alignment, which costs more money.
Yamaha is already shipping boats, dirt bikes, etc to their dealers so tossing a superjet on the boat/truck is just more costly than free, which is not how it works for these AM hull builders.
Also on economies of scale, the same materials and supplier discounts used for every other product applies to the superjet. Yamaha is buying insane sums of cables, wires and raw aluminum for everything else they are making, so these supplier discounts apply to all items they produce, not just the superjet. AM hull builders are not building dirt bikes, quads, UTVs, boats etc to distribute the costs across multiple product lines.
There's just so much missing from this...
$1000 in materials sold for $4000 is not a $3000 profit.
It's like when I used to sell tuxes and my coworker thought that it the tux cost $40 and we sold it for $200 that the company made $160. I had to explain to him what a power bill and rent are.
It's possible that the costs of materials is about $1000.
But they need someone to prep the mold, which costs money.
Someone has to prep the patterns, which costs money.
They have to infuse the mold, which costs money.
They have to trim the parts, which costs money.
They have to put in the inserts, align the bulk head, bond the halves, install latches and pole holes aligned properly, which costs money.
Lets not forget any OSHA style standards, which although they may not exist the same oversees, are still necessary, such has suits, respirators, air purifying systems, etc.
Skis produced oversees require them to be shipped across and ocean, which costs money.
They are imported, which includes tariffs, which is money.
You are charged shipping, but that is from the US based distribution, so they have to be transported from the boat to the warehouse, which costs money.
The warehouse is a facility which costs money.
They need someone to manage their web site, which costs money.
They need someone to process your order, like Visa or paypal, which costs money.
They need employees to fill your order, which costs money.
Completely leaving out the part where anyone with an education in business would take the time to analyze a supply/demand curve to determine which price point would maximize cost per unit to volume of sales. You did say "X" amount more sales but there are a finite number of buyers out there regardless of the price.
It would be nice if hulls were cheaper, but saying $1000 in materials on a $4000 sale leaves $3000 in profit is so far off of accurate it's kind of comical.
Oh, and btw, Yamaha is a publicly listed company. Their publicly listed financials say they have a 5% profit margin and an 11% return on equity.
Yamaha has 1.6 billion in revenue and a net income of 100 million. That means that after all the expenses, that if your aftermarket hull cost you $16,000, the profit per hull would only be $1,000 to the manufacturer. You know, if you want to compare them to the Superjet. So at 400% your proposed price Yamaha would make 33% your suggested profit.
https://finance.yahoo.com/quote/YAMHF?p=YAMHF
Oh, and pretty cool fact, yahoo is listing yamaha motors at a NEGATIVE 99% quarter growth YOY, but they still have all of those expenses, so their current operating margins are much much much worse than what's listed.