Saving for a horse is really no different than saving for any other big ticket item. A car, down payment for a house, retirement, etc.
Together my SO and I would probably be considered upper middle class. However, I would never, ever expect any of his earnings to finance my hobby. We pay equally for household expenses and retirement, the left over goes towards our respective hobbies. I’m more frugal in the sense that I hunt for deals, I drive an old car, I don’t eat out. Every month I review my budget. I have automatic deposits to my retirement account (that’s non-negotiable). I also have automatic deposits to another account, right now that’s savings for a new car. Then I have a regular savings account that’s liquid for emergencies. If I have extra money at the end of the month I save it somewhere.
I’m lucky that my mom also rides, and my parents own a hobby farm. I made the choice to take a year off between my undergrad and my post grad. I had a sweet gig as a groom, saved a lot of money. I purchased a well bred yearling and kept him at my parents for a discounted rate.
I worked through my post grad and had a good job upon graduation. At that point I could afford to pay regular board and for a trainer to help me start him. I was able to do most of the work myself. We’ve since competed in the 3’6” A/Os and a couple of national derbies.
He’s with me forever. I’m ok with paying board on him for the rest of his life, even if he had a career ending injury tomorrow. If he died tomorrow I would be able to use the insurance money to buy a young horse to start over with.