How do you suggest that event attendees become members to receive a discounted rate?

You may wish to add a link to the non-member rate to allow a participant to register as a member and receive the discounted rate.

It is possible to add a step to the registration process by enabling the member login option. This way, people who view the page can purchase a membership, log in as a member to register for the event or decide to register for the event without becoming a member.

This option is in the "registration process" tab of your event.

To learn more about this, see this article: Setting up the registration process.