I finally found a local source for citric acid. My local feed store has it in 410 gm (a little over 14 oz) packages. I got almost 6 pounds for $12 and some change. I also got a 50# bag of baking soda for $14, and they were able to get me a better price on muriatic acid than my local hardware store.
You guys might check your local feed store to see what they carry.