Aside from your cake/cupcakes, does anyone offer the option to sell the client gumpaste accents? I'm thinking particularly as cupcake toppers, this may be a good option to have for those that don't want to spend the extra $$ on cupcakes but still want them to have something extra on top.

What would you charge for something like this?

There are lots of people on Etsy.com who sell cupcake toppers. You might want to look to see what they list them for.

I sell gumpaste flowers and silicone molds on Etsy, and the hardest part is the shipping. I'd guess that the cupcake toppers would be relatively easy to ship without breakage, but make sure that you have good packaging before you try to ship things!