[quote]You'll need display port cables.
The most economical place I buy monitors from has been the Dell Outlet on refurbished monitors. Make sure you buy 3 that can rotate into portrait mode to give you more flexibility down the road.
I would be careful about running cheaper monitors in portrait mode. Most cheaper monitors use TN panels, which have fairly narrow horizontal viewing angles and even narrower vertical viewing angles. Using them in landscape mode may be ok, but portrait mode tends to exacerbate the issue with narrow vertical view angles (since they now become horizontal). If you are going to run portrait mode, I'd get a PVA/MVA or IPS panel based LCD. The downside is they tend to be significantly more expensive than TN based ones.
You are correct, I wasn't aware of the limitations but I've now experienced that first hand :-) It is annoying if you don't have them arranged just right and your head is in the perfect location to view them.