there are a couple good walkthroughs: http://lifehacker.com/how-to-create-the-ultimate-tech... for the general gist and https://www.youtube.com/watch?v=RcsKNryPAzw to see a video. That and my pictures should get you through it. The hardest part so far is setting up the raspberry pie. But that's essentially all you need. You can plug controllers into that. The parts list to get the raspberry pi set up is:

The case: Official Raspberry Pi 3 Case - Red/White Sold by: PHOTOTECH ~$8

The micro SD card: SanDisk Ultra 32GB microSDHC UHS-I Card with Adapter, Grey/Red, Standard Packaging (SDSQUNC-032G-GN6MA)