Yeah it's a huge difference when you pay for everything yourself!!
I had horses as a teenager but the horse I have now is the first horse that I've paid for 100% in every possible way. Vet bills and boarding and training and tack and brushes and starting everything from scratch.
It certainly does get pricey! I adopted my guy and he immediately needed x-rays and all these vet calls and it adds up fast!
For right now I buy most of my gear / tack at a consignment shop which I am SO lucky to have locally. I picked up a beaten up old saddle for $25 (and it miraculously fits him perfectly!) and stirrup leathers that don't match for $10
I'm going to keep buying as much as I can second hand until we both get to where we want to be and it will be worth investing in boots/saddles/etc. For now he is still changing shape and it's not worth buying those expensive saddles to keep forever. Dingy cheapo ones work just fine!
I spend most of my free time out with my horse so at least the fact that all my money goes into him doesn't bother me too much as I'm not missing it doing other things XD