All that I looked at including my modular corsair HX750W had them on the Edit; had it reversed disregard;
bottom unless they specifically stated that they were for a bottom mount orientation in which case they were on the top. It will still exhaust hot air, which rises to the top, but not as well.
If the price is the big issue, you could just flip it over of course.
If you notice, the small writing above the cord plug in is upside down, the fan can be top or bottom.