Most of the sea mushrooms in China are produced in Donggang and Zhuanghe, Liaoning Province. Because of the need of long-distance transportation and preservation, they will be coated with sodium sulfite, which is harmful to human health. It will also be soaked in formaldehyde, so please be careful when buying.
The price is not expensive. Some restaurants have this dish of cold sea mushrooms, which costs about 25 yuan. You can buy it in major hotels and aquatic products markets.