So I combined all of those ideas. I got a fish bowl and black aquarium gravel from Walmart. I already had some potting soil from my garden outside. The succulents I purchased from a local nursery and the dinosaurs I found on sale for a dollar at Family Dollar.
Succulents need a more desert like soil. So you mix equal parts potting soil and gravel first. Then plant succulents. Then cover the top in gravel. My dinosaurs were quite big so it took some maneuvering to get them both inside.
The kids have enjoyed peering into the bowl to check out the dinosaurs. And while it is inaccurate (the stegosaurus and the tyrannosaurus rex never lived during the same time period) it looks nice and continues to keep the kids interested in the sciences.