First off, yes calcium acetate is a legal substance. It isn't explosive or dangerous. 500 grams should be enough to make at least 3 cups because the solution needs to be 90% isopropyl alcohol. If you take 3 parts calcium acetate to 2 parts water, and then take that solution and mix it with 90% isopropyl alcohol, a little bit of calcium acetate will go a long way.
But there are much cheaper ways to make it that I've recently discovered. I'll update my hub after answering this question. Another easy way to make calcium acetate is with normal chalk, which is calcium carbonate. Take the powder chalk and mix it slowly into grocery store white vinegar, which is acetic acid. 4 parts grocery store white vinegar to 1 part chalk is the ratio. The result will be that the chalk and the vinegar will combine to create both carbon dioxide, which will bubble away, and calcium acetate mixed in water, which will be left over.
The easiest way to accomplish this is to start out with about 3 cups of white vinegar and then slowly add your chalk, stirring it so that it dissolves. Keep adding the chalk slowly until no more will dissolve. After that, you'll need to evaporate the excess water out of the solution. The easiest way to do this is to place the solution outside in the sun for a few hours, or until half the solution has evaporated away. After that, you need to mix it with 90% grocery store isopropyl alcohol.