ATI's FireGL and NVidia's Quadro line of cards are pricey mainly for superior support of advanced, expensive professional software- such as Maya and 3DStudio Max.
It takes a substantial investment into hardware and driver development to achieve good, stable performance for the variety of professional software out there. You're paying for that level of support and features. This varies greatly compared, to say, writing a basic OpenGL driver to drive Quake4 heh.
You may not need that level of card... depending on what your CAD needs are and the software used. If you want a lot of preview rendering and advanced preview vs. simple design, a normal consumer level videocard will suffice. Video editing will also work well on standard consumer videocards and will be more attuned to cpu, memory and disk drive performance than anything else.