How much are my horses worth?

My wife is a horse vet and people ask her this all the time..she tells them "whatever someone is willing to pay". The horse market has really gone down with the economy and WIllie Nelson getting the slaughter houses closed. Now there are too many horses running around.You'd think closing the horse slaughter plants would be a good thing....but now the poor horse are shipped all the way to Mexico where they don't have humane handling like we do in the US.