Low cost mylar space blankets could be used to fabricate an inflatable shell (like those mylar balloons) and heat sealed with an iron to shape fairly cheaply. No rigid structure required and could be inflated/deflated fairly quickly by using one of those big valves similar to the Aerobed. It would be an easy way to create a test bed fer shapes that might improve with a more rigid design by proving what worked or what didn't without a major cost investment.
Been giving this some thought and figured someone might chime in with their opinions...
Whatcha think?