Arrival to Ho Chi Minh City

The real estate agent did not mention that to secure an apartment you need to pay one month rent AND one or Two months bond. So if the 500 is you accommodation budget , you will need to bring in 1500 just for that.
Your estimation of 500/mth accom is on the lower end of the spectrum, so be prepared for that.
it does depend on what you want, serviced, furnished, with expats, with Viets.

1,000,000 a day living expenses up till then (hotel accom, food in resturants, incidentals) will be heaps as long as you are frugal. (eg 300-400,000 hotel, Pho for breakfast 30-60,000 each) Banh Mi for lunch 15-25,000 each)
Eat western food, pay western prices.
Though if you have to taxi everywhere that will eat up funds. eg Airport to Thai Dien ~250,000VND
http://www.numbeo.com/cost-of-living/co … ry=Vietnam
(some of the prices are a bit out, look at the higher end of each price range, especially in HCM)

Hope this helps a bit