The most economic option is to buy an "open tour" bus ticket from Saigon up north along the coastline with as many stops on the way as you wish. Several companies offer the service ("Sinhcafe" buses are legendary among travellers) and buses leave from Saigon on a daily basis. The bus will take you directly to a nice town/village with nice hotels/hostels so this is really an easy and inexpensive way to travel in Vietnam. I would save a lot of film to Hanoi and north in general which in my opinion is the most beautiful part of Vietnam.
Thanks, I will definitely consider this option as part of my plan.