I don't think food safe is a concern.
A lot of people put their bulk grains in (new) plastic or metal garbage cans, but they also keep the grain in the bags that the grains came in. You could probably fit two or three 50 lb sacks in one good sized garbage can. You would want to have a good secure seal to keep insects/vermin out. Metal cans have the advantage of keeping rodents from gnawing into the containers.
Other options include air-tight dry pet food containers (available at pet stores, but kind of pricey), screw-top lid adapters for 5-gallon buckets, foodsaver bags, etc. I believe I saw a post around here where somebody added some adhesive foam weatherstripping to seal up rubbermaid plastic storage containers.