Roy,
Price sounds right for small quantities, bag or 2. I prefer the Sodium Hydroxide beads over flakes, just my personal preference. Basically I think they are uniform in strength. I would buy from your nearest supplier to save on freight. Look around your area and you might find someone local. If you are going to make your own chemicals, order some surfactant (gelling agent) too. That will help the chemical cling to the surface you are cleaning. Oxalic acid, I believe comes in a crystal form sort of like sugar, at least what I have did. Don't mix it untill you are ready to use. I haven't used any citric acid before. David probably has bought and used more sodium hydroxide than you and I ever will. He would be the one to seek advice from about that. I think in larger quantities you can get it for less than 50 cents per pound.
Glenn