It's on page 45, when Indy is bargaining with Al-Kassah:
?You can learn nothing, if you prefer,? he hissed and
immediately began to smile again. ?Remember, it?s not
just the vase itself that determines the price. Look closely
and see it is filled with the answers to your questions.?
?Even then it isn?t worth a hundred dollars.? Indiana
considered briefly. ?I?ll offer you ten.?
?Ten?? Al-Kassah replied in a tone as if he had just
learned that he was an alien born on the planet Melmac,
abandoned here on earth as a baby. But his voice betrayed
that he was merely in the middle of an Arab trading ritual.