Yep, it's far. From
http://wikitravel.org/en/Nha_Trang:
The journey to Nha Trang from Ho Chi Minh City (Saigon) takes between 6-8 hours on the SE trains
Cam Ranh International Airport is only 30k from Nha Trang. From Circle Mapper:
SGN-CXR = 192 miles
HAN-CXR = 673 miles
So the thing to do is to fly into SGN and take a bus or train from there.