your not really gonna find a good case for 40 bux mate...
especially micro atx. they tend to cost more because of there small size and generally dont have good cooling due to limited internal space.
Fractal Design Core 1000 is probably 1 of the best around your budget(i think you might find 1 for 50 bux) as there £32 in the uk. its not stunning but it is better than most.
Nevermind I found the NZXT Technologies Source 210 case