Just get any a DELL XPS DESKTOP with minimum specs with a late generation i7, and then kit it out with what you need. You can get one for under $700, or even under $500 if you hit the right sale, it will come with 16GB of RAM, install another 48GB for under $160, it will probably come with a 1TB hard disk, you could swap that out for an SSD if you wish (A 1TB SSD should set you back around $100). The graphics card that comes with it will easily support 2-3 monitors. You can do almost the same with any "box", just I tend to find the Dell's a bit more robust for this sort of thing. So you can do/get what you want for under $800-900.