PSA: The pony might not be such a "seeing eye dog over fences" or a packer for anyone when he gets some groceries and care.
If I needed this type of pony, and knowing that he's at least 19 years old, I'd want to see him in good weight first. You have to answer questions about his rideability when he's not starving and what it takes to keep him healthy. Both determine his actual value. As it stands now, it would be hard for any buyer of this type of animal to know what they were getting.