I personally use polysaccharide copper and p-zinc from Horsetech, very cost-efficient. I mix the 2 at the ratio I need (I think it’s 3:2 zn:cu which gives me a 3:1 ratio) and then feed a small scoop of the mix.
I use UltraCruz Natural E powder, also very cost-efficient. Pellets are a cheap option too. Please note that their recommended serving size is 80000IU and their scoop holds 4000IU, so find a scoop that holds what you need
If you find your horse is E-deficient, then I’d highly recommend a bottle of Emcelle liquid E from Custom Equine Nutrition to get the level raised quickly. After that you can probably keep things stable with the above. Emcelle is the cheapest, by far, of the 3 water-soluble/nano-dispersed products. If your vet isn’t familiar with those forms, and says your deficient horse needs 6000IU, then you don’t need that much of Emcelle, maybe more like 4000IU, it’s just that much more effective. Cross that bridge if you get there, i’m happy to share a great flow chart that Dr Carrie Finno presented to the AAEP a couple years ago showing how to supplement based on blood levels.
There are also several human gel caps that are in the same price range, Puritan’s Pride might be one. Some horses eat the caps, some won’t. microIngredients used to be a great cheap option, but they went to synthetic E not long ago, so aren’t “in favor” any more lol
Uckele has cu/zn, but they add in some kelp which makes it very off-putting for a lot of horses, though mine didn’t care when I used it. HT was cheaper so I switched.
California Trace also carries the powdered forms
Custom Equine Nutrition carries a powdered mix
MadBarn has a 3:1 Zinc Copper product which is that ratio, also powder.
Yucc’ It Up has Hay Harmony which is a powder/meal cu/zn mix but also has biotin