If you have to ask why it's so expensive, you haven't researched it or the company enough. Some supplements are very expensive and, for that reason, are probably more of an advanced supp.
If you are asking such open ended and broad questions, it probably means you have a deficit in your basic diet/program/goal setting structure and need to square those away before you can supplement.
Think of it as a house. You have to have the foundation, bricks, mortar, roof, etc. (diet/program to meet goals) Before you can move onto what kind of lighting you're going to use in the bathroom (Indigo 3G or other advanced supps).. if that makes any sense.