What is your exact travel date? Anyway, from Singapore to Xiamen, connecting flights are mostly with transfer at Beijing and not flight via Kunming. Since direct flights are available daily between the two cities, you can take one direct flight instead and then by another domestic flight to Kunming. From Guangzhou to Mandalay, conjoint flights via Kunming are available daily. As for the airfare, u would better make an online enquiry with your departure date since the international airfare changes from different travel date.