To those that may be confused by the BO being able to keep the entire proceeds - the best explanation I can offer is that the person who owes the boarding fees is essentially trading the horse for the amount owed. From that point, the debt between BO and previous owner is forgiven -- it is then up to the BO to proceed with the sale of the horse to attempt to recoup the actual debt. If they are able to sell the horse for more, they gain the profit. The difference is not owed to the original owner because they are not part of the sale - they traded the horse to the BO to eliminate their debt.
Original Poster, have you looked into working off your debt? It might require several hours a week, but it might be your best option at thistime.