It's also very easy to find a room to rent for a month for $300 or less in HCMC, even right in the center of District 1. I'm doing just that right now, in fact, and have a serviced room in a very good location. It's been my experience that Hanoi is generally more expensive in just about every respect but I haven't spent as much time there.

Personally if I'm going to put up with the hassles of living as a nomad I want to reap more of the benefits so I prefer to stay in cleaner, quieter beach towns and enjoy the slower pace of life but some people like city life I guess.