The first book makes a point that the Tin Woodman's job was cutting
wood and selling it, and that he had to prove he could support himself
AND a wife, which was why he was so industriously cutting and easily
chopped up by the Witch's spell. "...She, on her part, promised to marry
me as soon as I could earn enough money to build a better house for her..."
In the second book (the Marvelous Land of Oz) it's mentioned more than
once, with respect to the ferryman:
"When the man reached the bank Tip asked:
"Will you row us to the other side?"
"Yes, if you have money," returned the ferryman, whose face looked cross
and disagreeable.
"But I have no money," said Tip.
"None at all?" inquired the man.
"None at all," answered the boy.
"Then I'll not break my back rowing you over," said the ferryman, decidedly.
And with respect to Jinjur's intentions to conquer Oz:
"Moreover, the City glitters with beautiful gems, which might far better
be used for rings, bracelets and necklaces; and there is enough money in
the King's treasury to buy every girl in our Army a dozen new gowns. So
we intend to conquer the City and run the government to suit ourselves."
And in addition to the discussion of the Scarecrow being stuffed with
money, the Tin Woodman makes the Scarecrow his Royal Treasurer.
In the third book, Ozma of Oz, Omby Amby is promoted, but has a concern:
"Then, Omby Amby," said she, "I promote you to be Captain General of all
the armies of my kingdom, and especially to be Commander of my Body
Guard at the royal palace."
"It is very expensive to hold so many offices," said the private,
hesitating. "I have no money with which to buy uniforms."
"You shall be supplied from the royal treasury," said Ozma.
Then, abruptly, in "The Road to Oz", money's been done away with:
"Money! Money in Oz!" cried the Tin Woodman. "What a queer idea! Did you
suppose we are so vulgar as to use money here?"
"Why not?" asked the shaggy man.
"If we used money to buy things with, instead of love and kindness and
the desire to please one another, then we should be no better than the
rest of the world," declared the Tin Woodman. "Fortunately money is not
known in the Land of Oz at all. We have no rich, and no poor; for what
one wishes the others all try to give him, in order to make him happy,
and no one in all Oz cares to have more than he can use."
So in three of the first four books, money is clearly present and used
regularly in Oz. It is only in the fifth book that it is done away with
(the fourth book, Dorothy and the Wizard in Oz, actually spends very
little time in Oz itself, so the topic doesn't come up. It might not
have come up in Road to Oz had the Shaggy Man not already established
that he had a particular interest, or rather DISinterest, in money.