If you are building a gaming PC I would not choose AMD over the intel i5 CPU he linked above. If you add $99 for Windows 7 64 bit version you will have a real nice gaming PC for any game on the market.
Here are some cheaper case options
NZXT GAMMA Classic Series GAMA-001BK Black Steel ATX Mid Tower Computer Case $39
http://www.newegg.com/Product/Product.aspx?Item=N82E16811146061
Thermaltake V3 Black Edition VL80001W2Z Black SECC $44
http://www.newegg.com/Product/Product.aspx?Item=N82E16811133094
Rosewill REDBONE Black SECC Steel ATX Mid Tower $44
http://www.newegg.com/Product/Product.aspx?Item=N82E16811147159