There's a rhyme that ends in "Pop goes the Weasel"|
I'm familiar with the "cobbler's bench" version, but it's not the one that first comes to my mind. I think that's the version in one of the Little House books, where Pa would play it for Mary and Laura, and the game was to see if they could catch when Pa plucked the fiddle string for the *pop*. But they never did; he was too fast.
"A penny for an easel" is a perfectly reasonable mondegreen. I think I sang it that way for a while, too.
The song has its own Wikipedia entry
, with many variations listed, and speculations as to origin and meaning.