I priced up Dapol to manufacture the 20 foot back in 2012.
From memory, it was working out at around £16k for tooling and around 7 pounds per, including packaging / box.
5,000 wagons would set a cost price of 10.20 sterling (about 12.50 euro)
Add shipping, marketing, some margin to make it all worth doing, and you're easily charging 25 euro retail, assuming you could sell 5,000 of them...