The least expensive way to get between downtown and the Las Vegas Convention Center is to walk. From the corner of Fremont and Las Vegas Boulevard, it’s a little more than three miles, which, assuming a 20-minute mile, will take you an hour or so each way.
The next least expensive way is to take the #108 CAT bus. It leaves from the Downtown Transportation Center, three blocks north of Fremont Street on North Casino Center Boulevard (formerly N. 2nd Street), every 25 minutes during the week and every half-hour on the weekends. It travels south on Main Street, cuts over to Paradise Road, stops at the back door of the Sahara, then continues just past the Convention Center and stops at Desert Inn Road. Cross Paradise to enter the center. The trip is scheduled to take 16 minutes and costs $2.
Pick up the same bus on the northbound side of Paradise back to the Downtown Transportation Center.
See the schedule by clicking here.
You can also pick up the new ACE bus (Gold Line) downtown at several different stops, including the DTC; it takes the same 15 or so minutes to arrive at the Convention Center, but as it’s a "premium" bus service, it costs $3 each way.
The Plaza is the cheapest place to catch a taxicab to the Convention Center from downtown. You're right on Main Street heading south and the cab can cut over to Paradise on Sahara. A cab ride from the Plaza to the Convention Center will cost you upwards $12 for the one-way fare, plus tip, depending on traffic.
For more information about free shuttles, the Las Vegas Monorail, and more, check out our Transportation section.