Normally, 8GB of RAM is fine for gaming and you need a good video card because in most cases it is Not up-gradable. The most disappointing answer on these Forums is the video card is not up-gradable on most laptops.
On Tom's Hardware Graphics Card Hierarchy Chart you can compare mobile video chips.http://www.tomshardware.com/reviews/gaming-graphics-card-review,3107-7.html
Can you find anything with an i5 and 660M video card in your price range? Or if you prefer 7870M (Radeon)