“Are you free tonight or will it cost me?” is a jocular example of a terrible pick-up line. “Are you free tonight?” is a pun on “Are you available tonight?” and “Will I have to pay for a dinner/movie tonight?”
 
“Are you free tonight…Or is it going to cost me?” has been cited in print since at least 1988.
 
   
Google Books
No Hang-ups III
By John Carfi; Cliff Carle and Greg Tenorio
Chatsworth, CA: CCC Publications
1988
Pg. 7:
Hi. If this is a member of the opposite sex calling, I have a question for you? Are you free tonight…Or is it going to cost me?
 
Google Books
Bombshell:
The Life and Death of Jean Harlow
By David Stenn
New York, NY: Doubleday
1993
Pg. 149:
Undaunted, Baer accosted Harlow. “Are you free tonight, or are you reasonable?” he asked.
 
Google Books
Sleepless in Bangkok:
A Novel
By Ian Quartermaine
Bangkok: Distributed by Asia Books
2001
Pg. 95:
“Are you free tonight or are you expensive?” Steven asked.
 
Google Books
How to Behave—Dating and Sex:
A Guide to Modern Manners for the Socially Challenged
By Caroline Tiger
Philadelphia, PA: Quirk Books
2007.
Pg. 36:
Are you free tonight, or will it cost me?
 
Google Books
The World’s Stupidest Men
By Rick Sutherland, Barb Karg and Diana Briscoe
Avon, MA: Adams Media
2008
Pg. 203:
Are you free tonight or will it cost me?
 
Google Books
Pick-up Lines:
Become A Chick Magnet
By Barry Hughes
Lulu.com
2008
Pg. 18:
Are you free tonight or will it cost me?
   
Google Books
The Machiavellian’s Guide to Flirting:
For Both Men and Women
By Nick Casanova
Bloomington, IN: iUniverse
2009
Pg. 88:
Hog: “Hey babe, are you free tonight or will it cost me?”
 
Twitter
Pervert Peter
‏@YABOYPERVERT
Are you free tonight or is it gonna cost me?
1:50 AM - 17 Nov 13