You can up it to a pretty high end A10 4-core or A8 4-core around the 3.8-4.2ghz range for $150, but to get a significant graphics upgrade you probably want to spend more like $200-300 on the card alone
You can go with more of a middle-high A8/A10 around 3.6-3.7ghz for around $100 and spend the other $200 on the graphics, if your budget is strict that is likely what you should do