Dzneynut is right. Only a select few pins stay about the same price. That would be the common, open stock/rack pins. But any LE pins can range from $5-$50. It depends on the rarity, character, and size of the pin. LE CM (Limited Edition Cast Member) pins are probably the best pins to add to a collection. One, because they are LE. And because ONLY CM's could buy the pin. Those are probably the most expensive. Also the older and newest pins relesaed I have personally seen to be the most expensive. But pins over time either get more expensive, or lose thier "initial" value. It really depends on the collector. I have noticed that Stitch, Nightmare Before Christmas, Pirates of the Caribbean, Tower of Terror, pins are extremely popular and therefore expensive. My advice is to try and buy them from the theme park for the $6.50-$10.50 because for a pin that will probably be the least expensive price to pay. (With exception to most non LE pins)
'Twas the Nightmare Before Christmas and all through the house,
not a creature was peaceful,
not even a mouse,
The stockings all hung by the chimney with care,
When opened that morning would cause such a scare,
The children, nestled all snug in their beds,
would have nightmares of monsters and skeleton heads.