Looking for inexpensive models for your fantasy and sci-fi gaming? Let's see what's in the Reptiles set in the Wild Creatures series at Dollar Tree.
You get 16 models, which is eight different models in two colors (red and black). Made from a stiff plastic with a slight rubbery feel.
Above, you can see ants (about 35mm long), another bug I recognize but don't know the name of (50mm long), and a type of beetle (30mm long). Some of these could take a standing passenger or two; the beetles could be pushing stones or dung balls, or pulling vehicles.
Above, I think it's a mantis of some type (40mm long), spiders (35mm long), and scorpions (55mm long). The mantis would look more threatening if posed in a standing posture, and might fit a 15mm rider. (They can also fly.) The spider could take a sitting or standing figure. Scorpions and spiders could add 'venomous' to your monster arsenal.
And finally, some actual reptiles! (Well, not entirely, because frogs are amphibians…) The frogs are 30mm long, the geckos are 50mm long. Frogs can represent evil gods, or just be venomous with wicked long tongues. And they hop. Geckos can climb walls.
I imagine you would want to at least do some drybrushing or add a wash to these, if not painting them entirely. I haven't tried, but I expect they would take paint well.