I use the same containers and even Master Batch my Lye Solution in them (in the sink because I'm not stupid). I also have a couple of dishpans I bought from the local Dollar Tree to mix up some larger batches. They work well if you are scooping the batter out of say a 14lb batch, but trying to pour more than 3lbs of batter is troublesome. They are great for mixing bath salts in.
You can also look for HDPE 1 gallon buckets...my local soap supplier carries them, Home Depot has them, a couple of the grocery stores carry them in the 'bulk' section.