Have you seen this stuff from Crayola? My sister gave me left-overs from my niece's school project. It's cheap, comes in different colors, and air dries quickly. When dry, it is very light weight. It holds details pretty well, too. I know it can be colored with markers but I haven't experimented with paints yet. The problem with marker ink is slow drying time.
The little piece I colored red left smudges on my fingers and the table. Once dried, Model Magic feels kinda like foamies. It doesn't break if you drop it but it was no match for Gunner the Pomeranian's teeth. (Note the gash above the lip of this little devil, who is also missing a horn after his run in with the dog. He faired better than his model magic brethren who were all eaten.) It's non-toxic but as dogs seem to like to eat it, I'd store it high if you have pets. Create sheets with a pasta roller and it can be stamped. I'm not sure super fine details would stamp but the chunky one I used worked just fine.
