This door opening is a non-standard height – about 6′ high as opposed to the standard 6’8″ opening.  The easiest way to replace a door of this size is to cut it custom from a solid wood door.  I used a solid core oak door so I could cut the size specifically to match.  First, though, I installed a 2′ x 3′ window with grid pattern (by Mastercraft from Menards) to allow more light into the room.  I think it looks quite nice, and at a total materials cost of about $125, you can’t go wrong!