Economy of Brave New World

The social structure of "Brave New World" implies that there is no need for an economy. In a world where there is no forward mobility and each person each person is not working towards a goal, I do not see the need for an economy. Economics are driven by Greed and selfishness but in "Brave New World" people spend money because they are conditioned to. It seems in the book as if the market needs constant stimulation but I do not understand why. In a world where an epsilon can be programmed to do any kind of menial labor, why pay them? Where is all of this money that goes into stimulating the economy of a stagnant social order going? I feel as if the only place all of this money could be going is into a dumpster somewhere. When there is money, there is the implication that people want to improve their lives in some way. However, the vast majority of the population cannot think further than "hungry" or "tired." The only people who might feel the desire to buy something new is an Alpha, and even then, they need very little after all of their conditioning. They are conditioned to constantly buy new things, and in a way, so are we, by the media and our society. But when we buy something, our money is going to another person who will then use it to buy something they need. Our money flows through people due to our greed. In "Brave New World" I simply do not understand how capitalism can work or why they need it in the first place.