Completely depends on the Pokemon on the card. A card's price is also affected by the popularity of the Pokemon on it since a lot of collectors, both the casual and the more serious, will covet certain Pokemon more than others. The "Charizard premium" is an observable affect that impacts prices of Charizard cards, even if the Charizard is not really all that good, since Charizard is a popular Pokemon. It also happens with other Pokemon, too, but generally less pronounced than it is with Charizard. I'm fairly certain that Mewtwo cards are more expensive than the exact same card (as in same HP, same attacks, same retreat cost, same set, etc) would be for a newer legendary like Deoxys.
Also the Dark Explorers stuff is still legal in Expanded in addition to some of the cards having reprints that are legal in Standard.