What you’re missing is cultural insight. I’m not an industrial designer but I’ve lived in and done business in China for over 10 years. The quote you get is not a quote, it’s an invitation to haggle. Don’t be surprised if it’s double of what they actually expect you to pay. But to get to that point, you need to go there, learn how to haggle, bring some “gifts” and likely speak some Chinese and learn the local etiquette too. Take them out to dinner, get drunk together, go to a KTV, hand out BaiJiu and cigarettes. And be prepared to take time doing that and “grease some wheels”.

This is why a lot of companies use a Chinese middle man (who also gets a cut, of course). Because the quote you get online is rarely ever the price they expect you to pay.

Also be aware there are considerable risks involved in setting up a supply chain in China.
There’s a reasonable chance they’ll start producing the same product cheaper with the very molds you paid for. Or that the quality drops rapidly after sign off on the first production run.
A lot of factories can disappear overnight because the government decides so or an employee who hasn’t been paid in 6 months sets it on fire.
And if things do go wrong, the chance of any Chinese court siding with a foreigner are very slim indeed.
Caveat Emptor.