I would suggest one of these cases for open air:
This one is plain jane, but works nice:
http://amzn.to/mzWGQRThis is from the same company but is stackable:
http://amzn.to/jPdb7eI currently use the Antec 300 for my rig, since my wife would kill me for running open air rigs
Amazon has them at a great price at around $59:
http://amzn.to/nykgpEThe Antec 100 is also a great case. Amazon has them for around $54:
http://amzn.to/q6hMx2