Why would you want a top-mounted PSU? That's less thermally efficient.
There are many cases like this. Just trawl Newegg, sorting by lowest price and starting around $50, and check out whatever isn't too flashy for you. "ATX mid tower" is a Newegg category.
On another note, good ventilation will be pointless if you stick the whole thing in a little wooden box in your desk. That could be a pretty serious thermal issue if you're doing a high-end build. Does the compartment have a solid back, or can the case exhaust? Can you post a picture?