From Yangon There is a night bus with air-con (there are 5 options, 17:00, 18:00, 19:00, 21:00, and 21:30 departures, standard 10,500 kyat, VIP 15,000 kyat, 8.5-9 hr) running into Mandalay. Almost certainly the cheapest option for getting between the two main cities in Myanmar.