You can definitely find new lights for a 75 under $700. The biggest thing with lights is knowing what you want to keep in the tank. Soft corals will demand less light than Large polyp stony corals which demand less light than the small polyp stonies. Do you have an idea of which corals you would like to keep? You also have to decide whether you want Metal halide lights, fluorescent (which there are a couple of different types), or LED.
As for adding livestock, IMO it is advisable to get your water tested and know where your levels of Ammonia, Nitrites, Nitrates, Salinity and pH are before you add anything. Once you add corals you are going to need to keep track of things like alkalinity, calcium and magnesium. (These levels are dependent upon whicj type of coral you choose to keep). Check out this link there are many good articles about saltwater basics: http://archive.reefc...threadid=102605