There are several factors you need to consider: your career goal, your age, your family, your financial strength (I am not sure how much is the UM tuition, but I feel the tuition plus salary loss is already more than 100RMB -- based on your current salary. Also the living expense and all kinds of expenses, e.g. health insurance, auto insurance, car maintenance cost, book cost, entertainment cost, etc., you have to consider many factors, which are not low either), and the area you aim at after MBA (do you have competitive advantage? is that hard/easy to load such a job with UM MBA? do you have any relevant experience?). Of course, if you can load a decent job or even those IB/MC job, you can easily get your investment back.
You can think all these factors before you make a decision.