Dedicated graphics Card die Linux VM?

To get a smoother display of my Linux VMs, I would like to install a dedicated graphics card. I am looking for a simple and inexpensive option. It should be energy-efficient and not actually have to display 3D applications. I still have an old, smaller GTX 970 lying around. I also have a GTX 570, that's what I mean. Which one can you recommend? What cheap and energy-saving alternatives are there?

Thank you.