Its pretty easy to make from Calciym Chloride and Sodium Hydroxide (Caustic Soda)
All the usual warnings about how dangerous NaOH is, I have a 20 year old scar that I will take to the grave so be careful and at least ware eye protection!
link that appears not to be a complete wank (some are very risky)
Should be a lot cheaper than the link above.
Mark
If you use Food grade CaCl from a home brew shop you should be OK, If you used Damp Rid there is likely to be enough contaminates (Cadmium being the worst) to be a concern if you need food grade. I wouldn't be too worried about the NaOH, just buy it at any hardware or supermarket, the way its made leaves it fairly pure as far as heavy metals are concerned.
M