RePEc is allowing free access to its services, to readers, authors and publishers. Why? Because we want that research be disseminated the most widely possible and in the most democratic way possible. Everyone should have the same chance at getting read, no matter where the author is located. And everybody should be able to access research, no matter what the means and the location.
Of course, we cannot make research completely free, as some publishers keep their material gated. But whenever possible, we offer alternative, open access versions to gated material. Those versions may not be the latest ones, but they are usually close enough and usable by readers.
But how can we make all those services available for free? For one, we have volunteers who are willing to devote some of their spare time for the cause. Also, the running of RePEc is decentralized to the furthest extend possible. For example, the actual indexing is done by the publishers (following these instructions). As they are the ones who benefit the most from being listed, they are willing to comply with our requirements. Thus the data input is costless to RePEc, and then the collected data is made available to those who would like to build a service with it. Again, volunteers create and manage these services at no cost to RePEc.