I'm not sure on pricing for Appian adapters. If you click on hardware at the top of this screen it will take you to a link where they are sold. I have no experience with Matrox so I couldn't compare Matrox and Appian, but Appian is an excellent product. Excellent tech support. No I don't get a kickback.
Actually I have two computers, 6 monitors total. I'm never satisfied with my brokers, so I'm changing my configuration around from time to time, but right now I have Real Tick with charts running on a couple monitors, Hold Brothers' Graybox software on another, Redi Plus on a couple different monitors, IB's TWS on 1/2 monitor, I might have a couple internet sites up on another for whatever reason.
I actually think monitors are like an addiction; you never feel like you have enough. If I could figure out where to put them, I'd probably have a couple more.