I know people with both and the horse is more expensive. You need to pay board unless you have enough money for your own barn and stalls. Their medical bills/vet bills are extremely pricey and finding a large animal vet these days isn’t easy. Lots of hay, they need to be taken care of, let out, moved around, brushed, washed. And if you’re going to also be riding? lessons, proper footwear and attire, saddle and all the things that go with that- the horse wears a lot. those things are expensive. My aunt has 3 horses, I don’t know how she does it.