If you want to overclock you need an aftermarket heatsink, as the stock wont take you all that far. The most I would be comfortable with on the stock would be 3.7Ghz, and even that's dependent on how hot it gets in your particular conditions.
CM Hyper 212 EVO. $35http://www.newegg.com/Product/Product.aspx?Item=N82E16835103099
I assume you have HDD, OS and CD drive? Because if you don't you will have to include them and it could kill your budget.