I've got over a thousand rounds to store. I need something very effective and at a very low price.
You only have over a thousand rounds???... Go to the shoe department at Wally world and ask the attendant to dig out the silica packets from a half dozen shoe boxes. I have my local store collecting them and evry so many months I go by and thew department head hands me a bag of five or six dozen packets. Baked in an oven for thirty minutes, they are as good as new. Ammo cans are $13 a piece. You can probably get you small amount of ammo in two cans and five or six packets from the shoe boxes is all you need when sealed up. Before you close the lid for the storage, rub a finger wetted with CLP on the rubber seal.
Preppers use 5 gallon buckets, fill them nearly full, then set a piece of dry ice (frozen CO2) on the top of everything. When the dry ice is nearly gone, they seal the top. The cold and CO2 gas displaces most of the moisture inside the bucket.