Like everyone else has said, brand new expensive equipment is not needed, nor is an overly complex system that monitors every single parameter in your aquarium. If you are on a budget, water changes and freshwater top-off is all that’s really needed. As for how to afford corals, the best advice I can give is to establish relationships with people in the hobby in your local community. People are always willing to trade or give you corals that they might have been trying to get rid of. Once you get a nice amount of corals in your tank, try to learn which ones grow the best, and start searching for those specifically and build up into the high-end versions of those corals. Then trade frags of those desirable corals away for anything your aquarium needs, and pretty soon you will have many different types of corals without having dropped loads of money.