[en] The effect of booster energy on the cost of the AHF has been investigated. Increasing its energy raises the cost of the booster but lowers that of the main ring, creating a minimum in total cost. It is shown that this minimum occurs where the apertures of the booster and the main ring magnets are simultaneously matched to the beam emittance. For high intensity (∼100 μA) boosters, such as LAMPF II, the minimum is quite pronounced. For lower intensity (∼25 μA) boosters, (such as the AHF) it is shallower and other considerations may outweigh those of cost in choosing the energy