“That’s what money’s for” (to spend it) is a popular saying. “That’s what money was made for, isn’t it?”  was cited in print in 1867. “That’s what money is for” was cited in print in 1871.
 
 
Chronicling America
11 July 1867, The Elk Advocate (Ridgway, Elk COunty, PA), “The Golden Test,” pg. 1, col. 2:
“You are spending money fast, Harcourt,” said his friend.
“That’s what money was made for, isn’t it?” said Harcourt.
 
Google Books
July 1871, Our Boys and Girls, pg. 426, col. 1::
“I’m nineteen, but I never had fifty dollars in my life at one time.”
“I suppose you are not careful of your money.”
“I’m careful to spend it as soon as I get it. That’s what money is for.”
 
13 December 1910, New Orleans (LA) Item, “Money and Kindliness” by Kennett Harris (New York Journal), pg. 9, col. 3:
“He never had no money, because he spent it as fast as he earned it. ‘That’s what money’s for,’ said Jim.”
     
28 November 1926, Greensboro (NC) Daily News, “Father Of Eight Girls Wishes He Had Many More Of Them,” pg. C9, col. 7:
“Girls are by far the best. I only wish I had another dozen. Of course, they cost more money to raise. But what of it? That’s what money’s for.”
 
15 September 1935, Seattle (WA) Sunday Times, “Seattle Native Son, Now 81, Recalls Boyhood Days Here,” pg. 19, col. 5:
“Well, that’s what money’s for—to spend. You can’t take it with you when you die.”
 
13 April 1939, The Adams County Free Press (Corning, IA), “Brentwood” by Grace Livingston Hill, pg. 9, col. 4:
“Oh!“Betty cried softly, sinking down on the lower step of the stairs, “you’ll use all your money up!”
 
‘Well,” Marjorie said happily, “that’s what money is for, isn’t it? To be used up?”
 
The Internet Movie Database
Marnie (1964)
Quotes
Bernice Edgar: Oh, Marnie. You shouldn’t spend all your money on me like you do.
Marnie Edgar: But that’s what money’s for: to spend. Like the Bible says, “Money answereth all things.”
 
12 October 1994, St, Albans (VT)

, “Dear Diane” by Diane Van Arsdale, Shopping News, pg. 9, col. 5:
I can’t tell you how much money she’s spent in the year we’ve been married on clothing alone. Her answer to me is, that’s what money’s for—to be spent!
 
Twitter
Dave Peckens
‏@DavePeckens
My Favorite Money Quote: That’s what money’s for: buying things! http://tr.im/hPQq
10:07 AM - 26 Mar 09