It's around 300$ the GPU, so 1800$
+ Motherboard, PSU and the rest you will be over 2500$
But that's just an example, it depend on many things : what kind of rig you want, how many and what kind of GPU, where you buy the parts ...
But for the entire setup. Including the Power supply kit,Metal frame for the Setup .It reach the value of 2800$.If you inverse so you will get the monthly payment as 330$.I am saying this payment with high cost Electricity. If the Electricity is cheap means, you will get 400$ as the payment. In 7 months you will get all the funds you spend for bitcoin.