Nutshell: Emergency Essentials has great prices and reasonable shipping on on Food Safe Buckets and Gamma Seal Lids.
I store most of my grain in 5 or 6 gallon buckets with Gamma Seal Lids. For recipe kits, I’ll store the whole kit (minus yeast and hops) in it’s own bucket. Gamma Lids come with two parts. An outer ring that installs semi-permanently on the bucket and an inner portion that spins off for quick and easy access. That means no prying off hard to remove lids. The whole thing is airtight.
My rule of thumb for grain storage is 5 lbs per gallon. With that estimation two 5 gallon buckets would hold a full 50 lb bag and two 6 gallon buckets would hold a full 55 lb bag (plus a bit more).
Gamma Seal Lids at Emergency Essentials