Which GPU (Graphics Processing Unit) is used to generate the graphics for avionics?
Real Aircraft displays do not use 'off-the-shelf' display adaptors. They will have some graphics processor (often developed by one of the major companies ATI/Nvidia) but this will often be an older/mature chipset. Each display also might have multiple graphic processors. The cost of an aircraft display is more closely related to the cost of developing/certifying the hardware/software than the physical cost of the components. You can't realistically compare an Aircraft display to your desktop PC.

Aircraft displays aren't just dumb monitors, each is a computing device in their own right that processes the data from the aircraft's systems. Each display will continue to work if another fails. Modern standards such as ARINC661 moves some of the processing/behaviour to other computing units, but the display unit itself is still responsible for drawing the graphics.