Hello - from what I can see the the domestic flights between Hanoi and Ho Chi Minh city in Vietnam is really expensive? Why is this...it's cheaper to fly via Kuala Lumpur than direct?
Actually, I see tickets offered by Vietjet and Jetstar are not too expensive, especially Vietjet sometimes offers promotional tickets with surprisingly cheap price. Although Vietnam Airline is a bit expensive but it's very safe and reliable.
You can refer at some cheap flights in Vietnam such as Vietjet air
You should flight directly from Hanoi to HCMC, you can book ticket at some cheap air such as Vietjet,