And i will agree with all above. Get as much RAM as possible for the amount of money you want to spend, it should be fairly cheap to put in 48GB, and a SSD to the disk cache. You will not want to turn back to the old setup when you start working with AE with huge amounts of RAM and a fast SSD :-)
...only thing is that cleaning the SSD disk cache is a all or nothing, you will have to loose 500GB perfectly fine disk cache because of 1 frame that AE cached wrong :-(