Mr.Anson, i want to state that the visa fees have no relations with the duration of saty. It is up to the entry times of visa. Multiple-entry visa is more expensive than single-entry visa. Generally speaking, the stay duration of L visa is 30 days. You need state the reason why you need stay in China for 90 days on the Visa application form, then the visa consuls will decide the entry numbers, stay duration depending on your situation.