The white pony was part of a paint your own release. I think (and I could be remembering incorrectly) she was a John Adams release...the same as the currently on shelves Fluttershy release. I also have a feeling she was UK released only. The US did get paint your own releases but the ponies were different and less well cast.
Lily, assuming she works, will be the $5 region but like many G3 she can be a hard sell.