My colleagues at Tom's Hardware have posted a review of the best sub-$800 PC for gaming. If you are building a budget PC, you need to read this review.
While it’s possible to build a very basic system that can do a little gaming for less than $500 or one that uses pre-owned / old parts for even less, $800 is the current sweet spot for building something that provides a solid mix of work and play, along with just enough oomph to stream PC titles to Twitch or YouTube.