You can buy buckets of copper sulfate cheap at farm supply stores or online. This is what I use as recommended by my farrier ( http://www.amazon
It comes in a bucket and is filled with blue crystals. Just dissolve as many crystals as you can in water and you have a cheap solution. Usually it takes them a while to dissolve all the way. One bucket lasted me for three years. I use it as a preventative and just spray on once a week. Also if your horse ever gets a crack in the hoof that dirt keeps getting in this stuff is good to flush it out and keep stuff from growing in the crack until it can grow out. Do be careful though as it can cause skin irritation if it gets on you.
Another cheap fix I have found that worked even better is raw honey. Sounds weird I know but it works. The honey must be raw honey. It does not get "tired" after a while like other treatments and will not harm live tissue. I have a horse with a permanent crack in one front hoof and the only thing I can do is keep the dirt and bacteria/fungus out of it. I dip a strip of gauze in raw honey and pack it in the crack. It keeps the dirt out and I never have to worry about infection in the crack.