You could build like a corner box inside of their stall on the floor. Horses by nature eat from the ground. It's easy and they seem to like it better. I have had the traditional hay racks that hang from the wall in their stalls. It seems all they wanted to do was tear the hay out of it and drop it on the floor to eat it.
My mom just uses hay nets, or a bucket secured to the wall. Just the basic shelf with 3 sides to keep the bucket from slipping placed at a reasonable height, then you can secure the bucket pertinently with bolts, or strap it to the wall so you can take it out to spray down every once in a while. Depends on how fancy you want it and what you are feeding.