JPSC, we do have a master topic for this, which HerpaDerp kindly posted.
The reason you should stick to that topic for all computer questions is because if nobody did, half of off topic would be questions about computers.
So your budget is $5000?
I definitely don't recommend buying that prebuilt that Nick posted. While it's a good machine, you can do much better.
Are you confident in building one? It is quite easy, pretty much a fragile jigsaw puzzle with 10 pieces.