I have an Aircraft Dispatch Certificate in addition to all my flight certificates and types. It cost approximately 7K and if you go to most airlines the pay starts at 10-12.00 and hour. Usually, you need to start small airlines before any larger 121 will consider you. Another possibility is to start in scheduling or some other capacity and transfer into the slot if it's offered internally. You do learn a lot about weather, reports, duty rules, ETOPS and the obvious flight planning. You usually have to learn how to do it all manually, just an EGB and pocket calculator for the practical test. The written is just a retake of the ATP.