Western food and luxuries have always been comparable to prices in their respective countries. How do you not know this? If you're talking about the 70s, then yes, it was probably much cheaper, but a bottle of Coke was also 5 cents in the US.
As far as the exchange rate, it fluctuates. How do you not know that either? Vietnamese Dong will also go up and down for yo ass. As young Vietnamese girls keep seducing old Westerners and East Asianers, and take half their <deleted> when they divorce or the man croaks, the country will keep getting richer and richer. So then, don't you think the prices of general costs will follow suit?
Vietnam's roads are <deleted>in' horrendous. I've seen busy intersections that simply has a barrel in the center of it, and people just wrap around the <deleted>. When diesel trucks are about to enter the intersection they literally do not slow down at all, they just honk their horn as to say "THE DEATH TRAIN IS COMING BITCHES MOVE OUT THE WAY TOOT TOOT". Sorry to say, but they are pretty <deleted>in' primitive and savage-like out there.
But enjoy your life there bruh.