I spend $1400 on my current rig and honestly I felt I over did it.
Back in 2006 a friend of mine went all in. He cashed all his overtime and bought the most insane rig I've seen with my own eyes. It had it all, and then some. It had just one monitor but still the total was $6450!
I got to visit him once and marvelled at the max settings of Oblivion. A few days later he was assaulted with a bat. Once he had recovered from his physical and mental wounds the hardware had literally nearly halved in value.