Zinc and castor oil nappy rash cream from the supermarket is excellent for superficial wounds or whatever you would use products like Potties White Ointment for.
Sulphur from produce stores instead of garlic in the feed - works better than garlic as insect deterrant, is cheaper and doesn't stop reoxygenation of red blood cells like garlic does with continued use.
Best mane and tail comb I've used is my fingers.
Don't use shampoo if you don't need to remove stains. Water and rubber squeegy repeated once or twice removes dust and dirt without removing the coat's natural oils. Coat, mane and tail come out lovely, soft and shiney and no problems of scurf from products not rinsed out properly or dry, itchy, flaky skin.
Save your tea bags from you morning cuppa and make up a cuppa with warm water to use for cleaning nostrils and wiping around eyes. Smells good, nice and warm but don't use it on light coats unless you don't mind a light brown stain.
The cleaning mits from the supermarket that attract the dirt (the ones that you don't need to use with cleaning chemicals) are great for removing the dust from coats and are soft around the head and don't tickle around the tummy like brushes do.
Old electric blankets from op shops are usually 100% wool, thick and durable, and the least expensive woollen fabric you can buy from anywhere. You just need to thread out the wires and if you want to felt the fabric just wash doing the complete opposite to what you do for you best jumper.
Tell your family and friends what you need. Yesterday got a queen size bed cotton mattress protector and queen size bed woollen fleece underblacket from mum that she didn't need anymore. She said to use it for Odin but thinking I will retire our bed's old ones for Odin and use her rejects for our bed.
Unwanted older style sleeping bags make rugs, Ususally satin or waterproof on one side and cotton on the other.
Make up cotton rugs from sheets for use under bigger, thicker rug. These can be swapped regularly, protect the thicker rugs from the body oils and sweat and are easier and cheaper to wash than the big one.
A good roll in just damp wood shavings is a great way to remove dust from the coat and give the hair a natural shine.
Free lease your horse to your local Riding for the Disabled (if it is suitable). They will house it, feed it, do daily care, and share vet expenses in return for its use. You still get to ride whenever you like because they generally use the horses during the times you don't. Its different for each centre but it's worth checking out.
Store your bales hay on a $3 tarp to catch all those lovely bits of leaf that fall to the floor and get spoiled.
Hardware store tool belt is great as a grooming tool belt.
Squeezy sauce bottles are good for products like molases and hoof dressing. harder to spill, easy to grab and use, doesn't hiss at the horse like spray bottles do. Just fill them up from from the larger quantities you can buy and store.
Simplify your medicine/first aid box, look into the old faithfulls, like sulphur, condy's crystals, pure honey etc.