Are you looking for cheaper options or just different options? I'm not going to dig into doing research but here are two more options:
Mandalay to Chiang Mai, then Chiang Mai to Singapore.
Mandalay to BKK on TG.
AirAsia...I believe you have to buy two tickets. When I flew Mandalay to Vietnam years ago, I had to clear immigration before boarding my second flight. I don't know if that is still the case today. If you still have to clear immigration and go to check-in again, then I don't think that 1hr45m will be enough time.