I'm trying to get a price estimate as part of a project to build an unusual scale-model solar system along a bike trail. This part of the project involves making a round ball with a diameter of exactly 11.35" inches that can be securely fastened to a wrought-iron fence. It looks like white Strong & Flexible Plastic would be our best bet with Shapeways (painted reddish since it will represent the planet Mars, since only white has a big enough bounding box), but I don't see a simple way to estimate the price. I'm guessing that to secure it to the fence, we'd need to make two hemispheres, then glue them together around the fence. But I don't know what sort of wall thickness or internal supports would be needed. It should be strong enough to survive being outdoors in wind and direct sunlight and snow for a few years, at least. Can someone with more experience come up with some back-of-the-envelope price estimate? Or tell me if this approach won't work for some reason? (Will this kind of plastic degrade if left outdoors, for instance?) Or if you have a better way to make a sphere of that size, I'd love to hear it. Thanks!