“Never/Don’t marry for money—you can borrow it cheaper” is a joke that’s frequently said to be a Scottish proverb (phrased “ye’ll borrow it cheaper”). The saying is first cited in 1910, when the wife of English author Anthony Hope (1863-1933)—Elizabeth Somerville (1185/6-1946)—said at a dinner in New York:
 
“Never marry for money. You can borrow cheaper.”
 
In 1927 and 1930, the saying was attributed to an English “Lord Dennison.”
   
 
Wikipedia: Anthony Hope
Sir Anthony Hope Hawkins, better known as Anthony Hope (9 February 1863 – 8 July 1933), was an English novelist and playwright. Although he was a prolific writer, especially of adventure novels, he is remembered best for only two books: The Prisoner of Zenda (1894) and its sequel Rupert of Hentzau (1898).
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Hope married Elizabeth Somerville (1885/6–1946) in 1903, and they had two sons and a daughter.
   
20 March 1910, Illinois State Register (Springfield, IL), “Short Stories About Persons and Things” by Estelle Klauder, pg. 6, col. 3:
Dear Money.
Mrs. Anthony Hope, the American wife (of—ed.) the well-known English novelist, is as celebrated as her husband for bon-mots.
 
At a dinner in New York during her American visit the young lady expressed her disapproval of mercenary marriages.
 
“Never marry for money,” she said. “You can borrow cheaper.”
 
1 May 1927, The Sunday Oregonian (Portland, OR), “Lady Astor loses fight for women,” pg. 3, col. 5:
Sir Robert Newman Favors.
Sir Robert Newman, a sponsor of the bill, said there is nothing criminal in getting married and women should not be penalized for doing so. Some of the leading women doctors are married and in the dramatic profession there are Sybil Thorndike and Irene Vanbrugh.
 
Macquisten, conservative, in opposing the bill, quoted Lord Dennison’s advice:
 
“Don’t marry for money, my boy. You can borrow it cheaper.”
 
15 June 1930, Sunday Times-Advertiser (Trenton, NJ) pg. 6, col. 6:
CHEAPER TO BORROW
Don’t marry for money; you can borrow it cheaper.—Lord Dennison.
 
Google Books
Racial Proverbs:
A selection of the world’s proverbs arranged linguistically, with authoritative introductions to the proverbs of 27 countries and races
By Selwyn Gurney Champion
New York, NY: Macmillan
1950
Pg. 73:
Never marry for money, ye’ll borrow it cheaper.
 
Google Books
Complete Speaker’s and Toastmaster’s Library
By Jacob Morton Braude
Englewood Cliffs, NJ: Prentice-Hall
1965
Pg. 45:
Don’t marry for money; you can borrow it cheaper. —Scotch
   
Google Books
Encyclopedia of Humor
By Joey Adams
New York, NY: Bonanza Books
1968
Pg. 196 and Pg. 366:
Don’t marry for money — you can borrow it cheaper.
 
Google Books
The Routledge Book of World Proverbs
Edited by Jon R. Stone
New York, NY: Routledge
2006
Pg. 293:
Don’t marry for money, you can borrow it cheaper. (Scottish)