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. A little extra precaution in the handling and care of all your horse and stable equipment will allow you to get the most out of it. Make the most of lesson time.