It seems that anything that has to do with climbing costs and arm and a leg, and simple climbing chalk seems to be no exception. The reason climbing stuff costs so much is because they are selling to a small market driving up costs. A way around this is to find another source that sells to a bigger market. With chalk this is easy. You can get a 2kg bag of Magnesium Carbonate Light for around $10-12 from any local pottery goods supply store. It will last you absolutely ages and is already ground up, unlike the block chalk that you can get.