What is the most economical hoof supplement with good results? 

Ive heard Plain Gelotin powder. 

Equine Relevare Hoof Dressing was the best I ever used. Nothing even close. I don't know if it's still available. If it is then try it. 

Renew Gold Glo

4 oz per day (scoop included), 7.5 pound bag is a one month supply for $49. No junk, no fillers, 100% active formulation. Non-GMO and guaranteed to work.

CEP Hoof Rx has all the amino acids + biotin & Vit E. It's great for hooves & so much more. I pay $110 for a bucket that has 136 scoops. That comes up to less than $25mo. Maintenance is 1 scoop per day. I'm not a dealer, but I have been a customer for years. 

I have my 24 yr old and my 23 year old on renew gold. I swear by this stuff. My 2 mares feet look like I paint them everyday. Both mares look wonderful body and coat wise. No one can believe they are 24 and 23. My farrier has commented on how nice their feet look.  Both are sisters.