In Lost, the Others are doing a lot of things which are highly expensive: Fake passports, the running cost of the submarine and communication. Some of them might get salaries (e.g., Tom is seen in expensive hotels when recruiting Michael); they have the resources to run fake companies such as Mittelos Bioscience, or to kidnap Locke's father. Widmore even accused Ben of being responsible for the fake crashed plane in the sea.
How do they earn money?
Well it never been explained in the show, how the Others got their wealth. One can only assume with the mystic power of the island granting it to Jacob as the protector of the Island for 2000 years, allowing Jacob to get out from the Island, recruiting various people and accumulating wealth through various means necessary, which is also not explain in the show.
The Others is the enemy of the Dharma Initiative, of course they are not the one who is supplying wealth to the Others. Dharma only come to the island in the 70s. Of course once the Dhrama is gone, the Others is using all the equipment and stations left by Dharma. And also the submarine of course.
