NHA is a small airport, served only by VN and your final destination. You can fly there RGN-HAN or SGN. RGN-HAN-NHA is probably a shorter trip but not necessarily cheaper. IIWY I'd look into Air Asia RGN to BKK (or KUL) to SGN or HAN first. VN will be way more expensive. Once again, do more research please. Maybe read this first: http://en.wikipedia.org/wiki/Nha_Trang