Not that much, less than $50. I have like 10 just sitting around in a chest

 

It's worth around 15 Ecodollars with /sell hand, but auctioning and trading can let you get perhaps 400-700 Ecodollars since they are fairly rare.(horse lovers will buy high)

 

they are not that rare compared to the number of horses, and are easily stolen. The price can vary a lot but they are hard to sell at any price (I have well over 100 accumulated over a long time and from lwcs ect.