Most of the areas to the North and West of the airport are decent and affordable areas. Stay away from the areas immediately South and East (St Ann in particular). Generally, outside of I-270 is ok. South of I-70 and West of Lindbergh(US67) is generally ok. You can find a 1br apartment for ~500-600 a month west of 270 between Olive and Dorsett.

I live in Maryland Heights right now. Its somewhat "multi cultural", but safe and reasonably priced. PM me if you want any specifics about places in the area.