well...for cad/cam don't expect too much from cards in the $250 or under..a good card will set you back at least 4x times that. BUT it really depends on what you are doing....are yoy using 3D modelling kernels or a just plain 2d? for 2D, even a TNT2 Ultra would be fine. If you want something with a little more punch, a G2 GTS will work fine for light duty 3D modelling and any 2D you can through at it.
For full bore 3d you will need something like a Wildcat or Evans and Sutherland, etc.....