The free shop has bestowed [item2=Lily of the Valley Plushie] upon me and I know not what to do

Collection items come out of collections costing 250 CSC so Id say about 25 - 30 million sp so Id stick in that range as that is how much that amount of CSC costs

some may charge more since they are only available 1 month a year tho but i wouldn't go over 35 mill.