Anything with an AMD Processor will be cheaper and naturally run graphics better than most stock Intels. 400 is a little low to get anything to run midlevel graphics. You could get a used one off craigslist and upgrade the Graphics card but then you'd need a new PSU most likely. The processor in a used computer that low would most likely Bottleneck (restrict full power of it) a new graphics card.
I work at best buy and here are a few things that would run most of the stuff you play. Could probably play Guild Wars 2 at better settings than your current laptop. I am not too familiar with the game but I know its recent.
http://www.bestbuy.com/site/pavilion...20a8&cp=1&lp=1 (Goes on sale for less than 500 sometimes)
http://www.bestbuy.com/site/pavilion...specifications
(this is an older model, similar specs but less storage, still plenty)
http://www.bestbuy.com/site/pavilion...specifications
(This is a laptop, it would be able to run it.)
http://www.bestbuy.com/site/essentio...2010&cp=1&lp=4
(by far best bang for your buck in store) may have to get it online, not sure if it is still in store, has a good A10 processor in it.
AMD's are always going to be cheaper because they don't advertise. With a 400 for a desktop (assuming you don't have a monitor you would need one as well) its going to be tough to stay around there trying to do what you want. I would get one of the A8 or A10 laptops. If you can find one with dedicated graphics that would be preferable but AMDs integrated graphics are much better than Intels and it will be hard to find Dedicated Video memory in that price range. Another option would be E-Bay, Craigslist if you can find something decent.
Anyways sorry for the wall of text, hope I helped.