Many thanks for the prompt. I might have got there in the end, but not so quickly...
We're still at the Prancing Pony, but the stable doors were opened in the night and every horse and pony has fled. Fortunately Mr Butterbur steps in and not only purchases a pony from Bill Ferny at the vastly inflated price of twelve silver pennies, but also offers Merry eighteen pence as compensation for his lost animals.
However...
"As a matter of fact he came out on the right side in the end. "
only one of the horses had been actually stolen, and all the rest were eventually found, and this included Merry's ponies by Tom Bombadil. Bombadil sent Merry's ponies to Butterbur, so he "got five beasts at a very fair price".