Calico does not refer to a cat breed. You will see cats of a certain cat breed that have calico coats and you will see random bred cats that have calico coats. Calico coated feral or sem-feral cats in the Mediterranean are commonplace. See for example Cats of Morocco (scroll down to see a calico cat).
So, the answer to the question "How much are calico cats worth?" is as follows:
- Where a purebred cat has a calico coat the price will be the standard price for a purebred cat unless the individual cat in question is a special cat (a champion) or a breeding cat. The normal price is around $500 or £500 in the UK.
- Where the calico cat is a random bred female cat the value is almost nothing. In fact the worth of a moggie cat is the admin fee at a rescue center. Courts sometimes value random bred cats at about $30 as I recall but an account of the emotional connection rarely made. Although things are changing.
- Where the calico cat is male and fertile (rare) the value may be high to an individual buyer. I discuss this on this page.