Can't help you with the price but if you don't want to throw money out of the window: Get rid of all shrimp and hermits before adding Berghia nudibranchs or they will end up becoming very expensive food.
You could also buy a peppermint shrimp in the multiple times I buy them they don’t go for coral and just for Aiptasia plus they won’t die nearly as easy ad nudibranches, if you do get one make sure it’s not a camelback though as they are a lookalike who only go after coral