There is a low profile 750 ti from GALAX/KFA² or Zotac which takes up one slot at the back of your pc but the cooler has a 2x height internally. However I'm not sure it would fit in there. There are also some low profile 7750 which would perform slightly better than the r7 250.
You could also take a look at Silverstone's ML05 -> http://www.silverstonetek.com/product.php?pid=411&area=en . It is a little bigger but offers more variety and has more width rather than depth.
You could also take a look at Silverstone's ML05 -> http://www.silverstonetek.com/product.php?pid=411&area=en . It is a little bigger but offers more variety and has more width rather than depth.