The amount of payment you are willing to give to a cheap hooker with leprosy; how much you'd would give your best friend for a blowjob from them
"I payed Betty two pennies and a half smoked cigarette for a blowjob, but only got herpes out of it."
A lesser-known variant of the phrase "a pretty penny" (i.e. very expensive).
That Aesop moisturizer cost me a penny and a half!