You aren't going to be getting a Nvidia GPU with a $500 budget, unless you get something a few years older and used.
However, CSGO is extremely low demanding, if you get the high end HD graphics like the HD 530 or Iris graphics, you can easilly push 60+fps at ultra settings.
However, luckily, there's a HUGE sale for this laptop at newegg.com which includes a GT 940M: http
/www.newegg.com/Product/Product.aspx?Item=N82E16834315302