Link
What I've linked there, would run most stuff to a decent level.
But that's with no keyboard, mouse, monitor, speakers etc.
Or
Link 2
That wouldn't be too bad either.
Don't forget, none of those prices include an OS, and you'd probably want to play around with a couple of the other bits included, i.e. more RAM, an SSD for OS & boot, and a standard HD for storage, installing games to etc.