eharmony is free to sign up, and there is no charge for Basic Membership.
With Basic membership you can see all your member profiles and filter within the Member Preferences you specify once you complete the Compatibility Quiz. In addition, you can view primary profile information about other members, send and receive Smiles and Icebreakers, and respond to a first message at no charge. Furthermore, you can browse anonymously and see who has recently visited your profile.
While there are benefits to being a Basic member, such as no time limit under this membership, there are far more advantages when you upgrade to Premium. You can find a more detailed description of the memberships here.