Is it this one:
A guy walks into a pub and sees a sign hanging over the bar which reads:
Cheese Sandwich: $1.50
Hand Job: $10.00
He checks his wallet for the necessary payment, then he walks up to the bar and beckons to one of the exceptionally attractive blondes serving drinks to an eager-looking group of men.
"Yes?" she inquires, with a knowing smile, "can I help you?"
"Yep, I was wondering," whispers the man, "are you the one who gives the handjobs?"
"Yes," she purrs, "I am."
Replies the man, "Well, then, wash your hands because I want a cheese sandwich!"