I'm all about saving money when/where I can. With the farm & as many nags as I have the overhead is pretty sizable.
I don't sell manure (too many farmers around here with livestock that give it away that people wouldn't pay for it, unless it was organic maybe) but I do let people come get it for their gardens. I don't spread the pile through winter so it's nice & broken down come spring. The trailer & truck loads that go out save me money because I don't have to put fuel in the tractor to spread it.
Things that are marketed towards horse folks that can be bought elsewhere. My favorite one of those, slick & easy blocks. All they are is a grill cleaner. Restaurant supply places carry them in large blocks for next to nothing. From one grill sized one I can cut 8-10 slick & easy sized blocks. Last one I bought was less than 2 bucks.
Buy what you can in bulk. A gallon of Orvus shampoo for instance, lasts forever! I also have a favorite discount store (it's huge, anyone in IN that hasn't made the trip to N. Judson to Bailey's, you are missing out!) I bought a ton of extra halters, they weren't super quality but for $3, I don't care. They get a horse from point a to point b just fine. Also got a gallon of betadine scrub for $2.99 last trip up there, 5 gallon buckets for 50 cents a piece, new heavy duty metal wagon hose reels (that could handle 200 ft of hose) for $15. I didn't get any (didn't need them) but also saw a few trips ago they had stall mats for $7.99. It's my favorite place to shop. I always come out with a huge cart full, like a Sam's club sized cart and couldn't tell you when/if ever I've spent much over a hundred bucks on a full cart. Now when they bought out all of the inventory from several Lowe's stores that went out of business...that wasn't such a cheap trip lol.
Life is like a camera. Focus on what's important, Capture the good times, Develop from the negatives and if things don't work out, Take another shot.