Kin Hubbard (1868-1930) drew the popular “Abe Martin Says” one-panel newspaper comic. Many sayings became widely quoted.
   
“When a feller says, ‘It hain’t th’ money, but th’ principle o’ th’ thing,’ it’s th’ money” was first printed on November 23, 1916.
 
   
Wikipedia: Kin Hubbard
Frank McKinney Hubbard (born 1 September 1868 in Bellefontaine, Ohio - died: 26 December 1930 in Indianapolis, Indiana) was an American cartoonist, humorist, and journalist better known by his pen name “Kin” Hubbard.
 
He was creator of the cartoon “Abe Martin of Brown County” which ran in U.S. newspapers from 1904 until his death in 1930, and was the originator of many political quips that remain in use. North American humorist Will Rogers reportedly declared Kin to be “America’s greatest humorist.”
 
Wikiquote: Kin Hubbard
Frank McKinney Hubbard (1 September 1868 - 26 December 1930) was an American cartoonist, humorist, and journalist.
 
Sourced
When a fellow says, “It hain’t the money, but th’ principle o’ the thing,” it’s th’ money.
. Hoss Sense and Nonsense (1926)
. Variant: When a fellow says, “It ain’t the money but the principle of the thing,” it’s the money.
.. As quoted in The American Treasury, 1455-1955 (1955) by Clifton Fadiman, p. 993
 
23 November 1916, Rockford (IL) Morning Star, pg. 4, col. 5:
“Abe Martin Says” 
Miss Germ Williams says, “Submarines may be all right fer folks that don’t care for scenery.”
When a feller says, “It hain’t th’ money, but th’ principle o’ th’ thing,” it’s th’ money.
 
Google Books
The Quote Verifier:
Who said what, where, and when
By Ralph Keyes
New York, NY: St. Martin’s Press
2006
Pg. 144:
“When someone says, ‘This is not about MONEY, it’s the principle of the thing,’ it’s about money.”
Indiana humorist Frank McKinney “Kin” Hubbard observed, “When a feller says, ‘It hain’t th’ money, but th’ principle o’ hung,’ it’s the money.” Hubbard’s axiom gets repeated often in various ways, and attributed to a wide variety of sources ranging from H. L. Mencken, Bill Clinton, Rush Limbaugh, and sundry Hollywood cynics.
Verdict: Credit Kin Hubbard.