To create a cost-effective lobby (waiting) area feature for Twilio Video using Twilio Sync, developers need to follow several steps. First, they need to create a Twilio Sync Service and document for each meeting, and expose an API endpoint `/get_token` that serves tokens for both Video and Sync. The server-side code checks if the video room exists and updates the Sync document with a "started" status when the host joins or more than one participant joins. On the client-side, the application subscribes to the Sync document's updated event and monitors for the "started" status, making participants join the video room once it's started. The developers can also add business logic to validate the schedule of a meeting before creating a video room and use the Status callback event webhook for Twilio Video to perform necessary cleanup actions on room-ended events.