The most interesting fact I’ve ever learned about five gallon plastic buckets is that In the third world, they are so valuable that it would be unthinkable to drill holes in one! Lucky for us, five gallon buckets are so cheap and ubiquitous in the western world that they can usually be picked up for free.
Good places to check are supermarkets, restaurants, coffee shops, farm stores and other food industry companies (call first to save a potential wasted trip.) If you obtain a bucket from a source that is not involved in food, like a gas station or hardware store for example, make sure your bucket is food grade HDPE (high density poly ethylene) before using it for food purposes.
Since I literally buy buckets by the dozen and need all buckets to be the exact same size and shape, I purchase them second hand below cost from a bulk soap retail company. We have in the past gotten buckets from a soap making company, which is a little riskier due to the possibility of lye residue. I pay $2.50 CAD per bucket for buckets made in Canada. I think in the U.S, you can get buckets new for around this price, but prices for most things are much cheaper there.
Since sometimes five gallons is too big, I get smaller assorted HDPE pails from delis, coffee shops, and small restaurants – or right out of recycle bins when I find them.