It will most likely cost you more than $300 to euthanize him through the vet an get his body taken care of. If the rescue that is asking for a $300 donation is reputable and willing to take him on then I think that is your best bet. Also, where in PA are you? I'm in central PA and I can also check around for you to see if anyone is looking for a light trail riding buddy or companion. I also know of a rescue in New York that is very good and really takes a while to ensure the horse is in good shape and finding them the best home that they can. Her name is Christine Wright and her email is equineLI@yahoo.com
. Feel free to email her an see if she would be willing to take him on. You would have to find a way to get him there but I guarantee he would have a good home and she could probably help you with some of the others that you need to rehome as well.