When I buy them from a company that I know well, it still costs me almost as much as the real stuff.... The same is true with Taser training cartridges....
In both cases, the engineering and materials that go into the "trainers" represents much of the cost.... same is true for folding training knives and good force-on-force sim firearms. But, the training is usually worth the cost, if it is conducted well.
-rJP