I'd probably start here: PC Part Picker Cases - Sub $60/ATX Full Tower/ATX Mid Tower ATX
From here, scroll down the left side of the page and look for other options you may want (Side Panel Window, Color, External Drive Bays, etc...)
Personally, I'd stick with Corsair, Zalman, or Silverstone, but that's just me.
just go to a reliable online retailer like Newegg.com.
in their case;
select Components > Computer Cases,
and then select your search options including size & price range in the left menu.
I'd probably start here: PC Part Picker Cases - Sub $60/ATX Full Tower/ATX Mid Tower ATX
From here, scroll down the left side of the page and look for other options you may want (Side Panel Window, Color, External Drive Bays, etc...)
Personally, I'd stick with Corsair, Zalman, or Silverstone, but that's just me.