It is often cheaper to book all of your tickets via an Agent in Vietnam, if your flights are within Indochina, it can be sometimes 20-30% (sometimes even more) cheaper than the actual website price. Prices on MEL-SGN for example one-way is $780 (no tax) on the website, while an independent agent can go for 20-30% less, plus sometimes you receive a complimentary return airfare domestically within Vietnam.