Looking for video card for Optiplex 755

My kids are crazy about Minecraft and they all want to use my more high end computer to play. This creates a problem because there are three kids and one better computer.
I found A source for Dell Optiplex 755 desktops at a good price. I know they are older and lower end, but they rank higher in performance than the laptops the kids are using now, so it's a better option.
The Optiplex has an Intel core 2 duo 2.6ghz and 4gb along with a sufficient hard drive.
I'm hoping that there is a video card I can get for under $50 that'll help their cause. I know you can go nuts with video cards but its just not in the budget nor would it be effective up against the CPU and all that.
Just wondering if there is value in a video card vs the integrated it has now.
Thanks for the help.