The gravity well is partially a cost and partially a benefit. By having low gravity, the capacity to manipulate objects is greatly improved but having at least some gravity enables a lot of manufacturing processes that would otherwise be complicated by the lack of gravity. One example is laser sintering which needs some force to hold the powder in place. This process in particular is beneficial as it is very heavily utilised in rocket engine production.

Also I agree that asteroid mining needs to happen however the moon would serve as a very good base of operations for such industries.