If you find yourself in need of transportation to Tijuana while you're in San Diego, Uber now has an option with its Passport service. The ride-hailing app will arrange transportation for a one-way trip across the border, all you have to do is select the Passport MX option with the mobile software. Getting back is a little more complicated, though.
Uber operates locally in Tijuana and you can hail a car through the app that will take to you to the border. When you get there, you'll have to walk across and call for another ride in order to complete the rest of the trip. In terms of cost, depending on where the service picks you up in San Diego, you'll pay between $90 and $160 for up to 4 passengers.