The cost of manufacturing a product in China is dependent on a number of factors. The kind of product you're making, whether it's generic, customized, or completely new, the kinds of materials you choose to use, and how many product units you're ordering will all impact the product pricing.
In general, the more units your order, the cheaper per unit you'll receive. Many suppliers in China will have high MOQs (minimum order quantities), so some factories may not even consider making products for you if you don't plan to order enough.
Keep in mind that all pricing, including MOQs, are subject to negotiation. Many businesses new to manufacturing products rely on third party experts (like Kanary) to make sure the best pricing and terms are negotiated.