This guide over at ExtremeTech shows how to build a very capable PC based on the very capable AMD X2 chip for about $1,200--$1,600, depending on what you reuse from your current system.

Man, what a contrast from the old days--the original IBM PC would be about $6k in today's dollars--for a floppy-based, 16Kram, 5MHz text-based monochrome system!