first of all dude , if your planning to play 1080p resolution , it will be impossible to have a gaming PC that will run hardcore games at ultra , but if you want to play atleast high or medium here are the specs I recommend to you
processor
- intel i3 - $100
mobo
- any mobo that supports lga 1150 - $100
ram
- atleast 8 gb or 16 gb ( the price of 8 gb of ram is $100 while 16 gb is somewhere between $130 )
GPU
- GTX 650 Ti Boost -$200 ( its the bang for buck on gamers on budget trust me , It can play games on high most of games on ultra )
casing
- any casing - $80
PSU
- 600 watts - $50-$80
thats it! if you will follow this build it will cost $630