According to the Society for Animal Protective Legislation, the average cost of having a horse humanely euthanized by a Licensed Veterinarian is $225.  This includes the costs associated with the safe disposal of the animal's carcass.

The cost of maintaining a horse per month is $200 or $2,400 per year.  So the cost of disposal of an unwanted horse in relation to the cost of ownership is negligable and considered part of the responsibility of the owner. 

As a horse may pass from owner to owner and in many cases become devalued, it is important to consider the economic impact on those who become the final owner of the horse.  Responsibility begins from the moment of the breeding decision, with the knowledge a living being is being created and must be cared for, until the time of it's death.  As each purchase ensues for the horse in it's lifetime, it's care and disposal must be taken into consideration on the sale price of the horse each time.