Simple, easily printable Hot Wheels displays. Has space on the bottom that's left blank, allowing for customization. Small feet on the bottom slide into spaces on the top, allowing for easy stacking, or display on their own. Also includes a small indent for the wheels to prevent the car from rolling around.
20% infill worked fine for me, you might be able to get away with less.
If you don't have access to a CAD program but want one customized with a car make/model, shoot me a message and I can make one if I have the free time (depending on work/life stuff, this could be a while).