Yes Andy, you're right about the hotel prices in HCMC - they're very high especially for a developing country.
The topend ones cost well over $200USD a night. These are mostly in the deluxe part of District 1 but there are quite a lot of cheaper options not far away and these range from about $30USD a night upwards for budget level and midrange starting at around 60USD.

You could try this travel agency which I used for our HCMC hotel .....
Start off with the usual three w's then saigonhotel-link then dot com.
Click on accommodation and you can see Budget, Mid Range or Top end hotels.
There are quite a few decent budget ones but just bear in mind that a lot of them won't have lifts or are in very noisy streets. If either of those things could bother you, suggest you ask one of the consultants at the above travel agency to clarify or check out some of the reviews on travelfishdotcom

You can book online or call them (they're open till about 10pm Vietnam time - phone number on the website).