You would need $380 for this.
It's a budget build but I included some decent parts, the Phenom processor is decent and can be overclocked to meet your CPU needs for minecraft and the HD 7770 is a good enough GPU to get started with.
http://pcpartpicker.com/p/1i0Yk
I have absulutly no idea how to build a computer
You can cut costs on things like the amount of storage down to like a 250GB or be cheaper on certain parts but all in all this has the base performance you'd need.