How To: Make a fake pregnancy belly prop on a budget

Hey,

I'm a costume designer for a theater, and I have been hunting everywhere for either a realistic-looking pregnant belly to purchase that doesn't cost an arm and a leg, or a tutorial to make one. The belly is never seen not covered by clothing so it doesn't have to look like real skin or anything, but the actor is very energetic in her movements, so something soft like a pillow will not work because it will get deformed too easily. Also, the belly has to last through about 20 - 25 performances, so it has to be very durable. Any suggestions would be greatly appreciated!

Thanks,
Linda