So that's almost 6 pounds a day per animal? That is probably why your feed bill is so high. I know donkeys are usually really easy keepers, so they don't need much for maintenance. Have you ever considered a ration balancer? Yes, one bag is $30. But, you only feed about a pound of it a day per horse. So one bag may last you 10 days. That would be around $90 a month on feed rather than $160 a month for the All Stock and it's a lot healthier for them!
If you have horses that are hard keepers or need to gain weight, you can supplement with beet pulp or rice bran. Rice bran you only feed about a pound a day so that's cost effective. Beet pulp is very light weight dry and holds a lot of water when you soak it so it can help hydrate a horse if you have one that's reluctant to drink. I personally feed Purina Enrich 32 to my colt who is on a coastal/jiggs hay diet with about half a pound of alfalfa pellets. If you feed alfalfa exclusively, I believe you would need to feed Purina Enrich 12 as it has a lower calcium content. I know for a fact Gulf Tex on Spencer carries Enrich 32 as that's where I buy it. Steinhauser's in Alvin also carries it.