Interestingly enough, there seems to be one more FS original series Rarity on Amazon through a third party seller for 55 dollars.
Using my very unprofessional pricing skills:
I did find the original accessories for Rarity for under 10 dollars, and there doesn't seem to be much of a difference between the molds of the fashion style releases at a glance. However, someone is probably a lot more nitpicky and will be able to distinguish a 2010 release with a 2012 release.
Didn't find anything for Fluttershy, so these things are either elusive or just get mixed in with the standard "old ponies that my daughter doesn't care for anymore" listings that aren't easy to find ponies due to lack of tagging or names.