More expensive modern breast forms are designed by computers and can even be attached to the chest. They can be worn with strapless dresses and lingerie, while bathing, sleeping or even during strenuous activity.
And expensive breast forms CAN be...they can run anywhere from 5$ for an unweighted foam or fiber-filled "falsie", to several hundred dollars for a premium off-the-shelf weighted silicone form to several thousand dollars for the better individually designed, created and fitted custom prostheses. As one retailer put it to me:
"...you can pick up a cell phone for less than a hundred dollars and they have a LOT of technology invested in them. Then a bag of silicone goes for an average of $250??? Something is amiss!"Possibly.