Steve,
Probably 30 cupolas or more to make a resin casting practical. About what you can get from a mold before it needs to be replaced. Obviously the greater the number we make the better the price as we can amortize the master and the molds over more items. We, however, do not make a product and try and sell it, rather we make a specific number to fill orders on hand and then stop procduction.
Hope this helps,
Gerry