I am a nutritionist, and have formulated minerals for deer and cattle for years. There is very little difference in their nutritional needs. I'd pick a standard salt free beef range mineral that is popular in your area, mix in 25% - 50% salt, and place it in some kind of feeder pan. Cheapest and very effective.
A cattle nutritionist will have already determined the trace minerals required because of the soil types in your area, which might include things like copper or selenium.
Use the 1:1 ratio of calcium to phosphorus if deer have access to legumes like alfalfa, 2:1 ratio of Ca:P if they don't eat legumes much but eat a lot of grain. Not complicated.
