Price guides for Pokemon cards can be found online for free via various websites that specialize in buying and selling cards. Prices vary depending on edition, condition and whether the Pokemon card is holographic or not.
The value of a Pokemon card is dependent on a number of factors. The most valuable cards are 1st Edition Base Set Pokemon holographic cards. Shadowless cards refer to a run of prints that featured thinner text for HP values and attack points. They also do not contain the drop shadow behind the picture of the Pokemon that only becomes apparent in the later Unlimited Edition.
As a result of Wizards of the Coast still working on the aesthetics of cards during the 1st Edition and Shadowless eras, Shadowless cards are prized for their rarity and close proximity in production to 1st Edition items. A holographic Base Set Charizard card can sell for up to $80.