You're welcome

$2000 is plenty - You don't need top of the line cases or high-speed RAM or terrabytes of HDD storage so that saves some money. Just another consideration - sticking more than 2 graphics cards inside a computer is difficult due to heat and space considerations. It's possible if you use risers and rest a card against the case; this is why some people make miners in crates --> http://www.cryptobadger.com/2013/04/build-a-litecoin-mining-rig-hardware/.

Else, just buy 2 graphics cards and leave it at that. Depends on how confident you are with computer parts, I suppose.

But for $2000....you could almost look into building 2 computers with 2 cards each...and if you were keen, add a 3rd card later on using a riser. Your choice.