The pokemons value is in the eye of the beholder, for example:
-someone who loves pikachu may pay excessively for one because they love them, not caring about the price.
-someone who just wants any pikachu to complete the collection, may jump from person to person trying to find the cheapest one.
2 drastically different prices, because it's worth is completely different for those 2 people.
NB//
also, wouldn't that kind of kill the marts bidding system?