Take a look at this:
http://pcpartpicker.com/user/TotalInsanity4/saved/zHG3CJ
It should be enough for your needs. Inexpensive, reliable parts that are capable of overclocking to 4.5GHz under the right conditions and a GPU that when overclocked will crush emulation and play games at mid-to-high settings for the next 2-3 years
If you want a build that can't overclock but uses a better GPU, let me know. And keep in mind that if you make a trip out to a Micro Center it will probably end up shaving around $100 off of your total cost