There was a whole slew of MIP charms on ebay several years ago which has really brought their prices down. They usually go anywhere from $4-8. Looks like yours have good symbols so I'd say on the higher end if they don't have brown spots. Also, the one in the middle on the bottom is technically a Charmkin and not a Mommy charm although a lot of MLP collectors still want that one, anyway!
To my knowledge, none are more rare than others but someone else might have a different opinion.