My third build targets a mini itx form factor pc with a mounted GTX 680. I would like cases similar to the dimensions of the SilverStone Fortress SST-FTZ01 with the option to mount a ATX factor GPU. However my budget is under half the price (~£30-40) for a case. The cases listed here are all out of budget 
Any help/advice is welcome! Thanks in advance!

Any help/advice is welcome! Thanks in advance!