$300 budget build for League of Legends only

I only have about $300 and I want a computer that can run League of Legends with little to no lag(at least 40 fps) and I don't care if I have to put the graphics settings to very low and I already have a monitor, keyboard, mouse, speakers, and os. I'm only gonna use this computer mostly for League of Legends and not other games and probably a little web browsing. So please tell me specs for the computer and thank you in advance.

Your going to be extremely limited in what you can get for that price.... 


Do you need everything? What parts do you have now?

i have os, monitor, speakers, keyboard, and mouse and i thought league of legends didn't need a huge amount of power to run.


APU build with speedy 2400mhz ram.