Maybe you can find a place that will keep your horse for free or a reduced rate for the use of your horse when you're not around. Board for others. If you are lucky enough to have your own farm, you can consider caring for others' horses or renting extra pasture space. Make sure you check out all the legal aspects of this. Go second hand.
Used items can be just as good as new.
Buy at auctions. Some tack shops carry used items. Be on the look out for horse people changing disciplines, getting out of the horse business, or who are rich enough to buy lots of stuff. Take care of your equipment. Even leather that is not so top quality will last a long time if kept clean and properly cared for.