I am far, far from rich. We run a 15 horse rescue completely off public donations. We do not have any excess of money.
But we have a 32 year old blind, appaloosa with reoccurring abscesses. He lives his quiet happy life in our barn, enjoying 5 buckets of soaked hay cubes a day, as his broken teeth can't manage real hay. When the weather is perfect and he can totter himself outside he goes out and lays in the sun. That is his second favorite thing. His first favorite thing is to have the little girls who volunteer with us crawling all over him, itching his itchy spots. Over the winter we were unable to find a farrier that had the patience to do his feet, you need to do them a little at a time, moving on to the next hoof when his opposite leg gets too tired, just circling him until they're all done. He began to lay down a lot which was beginning to cause pressure sores. I found a old memory foam mattress and cut sheets of it and sewed it into his blanket. He never got a pressure sore. After a few months we gave up finding a farrier to do it, instead we found a farrier who would tell us how to do it. While he was laying down we fixed up his feet ourselves. From then on he was up and the life of the party again. He greets all our visitors and teaches all our new volunteers how to groom, he lives every day in happiness, but not always total comfort.
We do not euthanize horses who have become 'inconvenient' or used up. We will/do euthanize our horses when they decide they have completed their mission with us and are ready to move on.
I don't expect other people to be as devoted as us. We are quite extreme, we have 14 other used up horses who will live out their life with us. But do NOT tell me you had to get rid of your horse due to money. I am raising 2 horses myself, both rescues, on the income of a riding instructor. I make ends meet by being careful with my money. They don't have the nicest tack, but what they have fits and works.
And Honestly people, no horse gets completely crippled due to arthritis overnight! That is a slow progressive illness that takes over their joints slowly. When you notice this beginning to occur with your horse there are a large number of things you can do to slow the progression. Or if you find your horse developing it and know the horse is only going to get worse and you know you need them for heavy work like barrel racing do the horse a favor and rehome it before it's completely broken. If she had sold that horse before he was completely lame he could have been a school horse, a pony ride pony, a little kids first horse, who knows? He could have moved on to doing something like low level dressage, something that utilizes his joints in a different way so he would last longer. Rather than having a 14 year old horse (he could have had another good 10-15 years) be thrown out to god-knows-where, she should have recognized that she wouldn't want to care for or wouldn't be able to afford the care for a horse she can not use. She should have done right by him before he was completely used up.
I completely understand if a horse is unable to do the job you depend on them to do that they need a new home. But if a horse is beyond repair there is no place for them to go. If a horse has devoted a chunk of his life to bettering your life, you owe it to them to give them a peaceful end of theirs.