Not-a-historian, but from what I gathered, the story comes from oral tradition.

I somehow doubt this happened, despite Vlad's cruel image, one gold/silver coin seems ridiculous.

Principles are a powerful thing. :)

Don't forget that he tortured, impaled or killed in various other ways lords, peasants, women, children, ambassadors and merchants for reasons ranging from conspiracy and treason, to (petty) theft, adultery and lack of chastity.

Not to mention it is generally thought he derived pleasure from watching impalements - one account mentions he tortured and impaled birds and mice while he was imprisoned in Russia (or whereever).

He was a sadist, simply put. In modern times, I wouldn't be surprised if someone diagnosed him, locked him in a padded room and put him on a cartwheel of medication.