Have him euthenaised at home, in surroundings he knows.
Every time we buy a horse, we know it is heartbreak on legs. If you cannot afford to keep him, then why risk him going somewhere and being buted up and ridden? The best thing to do is have him PTS.
Owning a horse is like a marriage - in sickness and in health. Either way, we owe it to our horses to do what is right for them, however difficult and heart breaking that decision may be for us as owners.