Greenlights:
Here are some inputs:
I lived in VN for 3 and a half years. I loved it, but only because I was not on a 2500USD salary.
A decent accommodation costs around 1000 USD. You can go for cheaper, but if you are not from Asia, I can guarantee you, that you will not even survive 6 months... (cheaper flat: no aircon, noise, pollution, smell, no window, mould on the walls...)
After a while, SGN wears you down. 5 weeks, and you NEED some rest. This includes beach or mountains. A hotel which caters for an expat in VN is expensive (150USD+/night) Guaranteed, you can go cheaper, but than the few days off makes you wish, you were back in SGN (you pay 25 USD for no aircon, noise, garbage everywhere, smell, no service in restaurants, just nervous giggling...)
Food: yes, you can survive on 2USD/day, but in that case, you have no idea, what you eat (think Chinese chemically enchanted rice and beef (made out of pork). If you want a decent meal, that will set you back quite a large sum (from 2500USD). Local food is good, but once in a while, you want something closer to your taste. And that is expensive. In VN, you can pretty much could get whatever you want, but everything has its price.
Flying: fun. I miss that a lot... You learn, how to be legal, efficient and SAFE. But that is up to you. After a few sectors, your survival instincts will kick is.
Do not underestimate the cultural difference. It is truly a shocking experience. At least if you earn a decent salary, you have a reason to stay. If you get 2500 USDs, you will be miserable after the honeymoon period is over.
As I wrote, I loved it there, but the 2500USD difference in salary does not justify staying there. I was working for VNA. I had no problems there, but SGN is not for the faint hearted. I would go as far as saying that in some regards, life in HAN is much easier. VN is magnificent for a holiday, but a nightmare to live there. (of course, there are a few, who would disagree, and I completely understand them as well.)
And I could go on and on...