One option is to look up the ingredients in a product you like and buy some of those ingredients to make your own.
Another is to look for a company that sells ingredients for making stuff in your country and see if they have a recipe (many of these companies provide free recipes and some have pet recipes). You could also modify a human spray in hair treatment, or search for a horse specific recipe online.
Not sure how up to date these links are, but this website has a list of different cosmetic ingredient suppliers in various countries:
Cosmetic Ingredient Suppliers.
Making any sort of product for humans or animals is really easy, and most of the commercial stuff you are just paying mainly for the packaging, marketing, etc. Most products are mainly water and the cost of active ingredients is really low. I have made all our human and dog conditioners, washes, moisturizers/balms etc for years. I do have a chemistry background but I don't think you need lab experience as it is all very easy. Usually melting a water phase and an oil phase and mixing them together with an emulsifier and a preservative (required if it contains water as otherwise things go moldy; you can get organic certification approved preservatives if that is a concern). Most recipes say to use a stick blender, but if you do not have one, I use a hand-powered egg beater and it works fine (you do not need to mix it continuously; just on and off till it cools). When I make our moisturizer, it cost me about $4 to make what would cost $40 to buy as a ready-made commercial product.