Now the DragonballZ comic con 2014 P4 promo card seems to have separated a bit from others and goes for around $15. P5 can sell for $100 or more.
If the cards are in the same quantity, there must be some other reason for the value of the P4 card increasing. Perhaps it's a popular character in the game. (I know nothing of DBZ, pretty much except that it's abbreviated "DBZ").