Computer Question(External GPU's)

Hello steamgifters. I have a computer question today. I am looking into getting an external video card for my laptop as it has pretty bad graphics and I don't have quite enough money for a full new laptop. My price range for the external card is around $100 since it's just one piece of hardware.

What are the best external cards for that price range?

Will any external card work on my laptop?

Do you know of any issues with using external graphics cards?

Thanks for your help!