I'm currently running two monitors on my PC using a video card and not the on board video which appears to be disabled when the extra card goes in. The card has three connectors but when you plug three monitors in only any two of them can be used. Windows recognises all three as does the video card driver but it can only display a picture on any two of them.
So, what's the cheapest way of being able to use all three monitors? I don't game, its just a bit of light CAD, SketchUp plus email or whatever.