You can start anytime. there is no problem for that. For the price, I think it's better to talk with him yourselves. The price will depend on how many students he has at the same time, and how private the study you want. For example, you only want one to one study, or don't mind have some hours share with other students,(if he has more than one students) And also depends on your own requirements of course. If you do interested in it, I can give you his email address or telephone number. You can talk with him in Chinese. He really is a very nice guy, by the way.