In his discussion of the Siege of Paris 1870-71, David McCullough in The Greater Journey discusses the path of meat prices. One observer “considered cats ‘downright good eating,’ as apparently did many people. The price of a cat on the market was four times that of a dog.” Whether the price difference was really based on demand—differences in tastes for the two kinds of meat—or supply—is not mentioned in the book, but perhaps Parisians protected Fido less well than they protected Fluffy.
This illustrates a ubiquitous problem in discussing price differences: It’s easy to adduce a cause on one side of the market, but just as easy to bring up another cause on the other side of the market. I would bet on demand in this case, though, since it’s easier to protect Fido than a loose-running cat.