A Tijuana based tour company, in operation since 2009, Turista Libre offers interesting trips into Mexico. With them, you get to experience everything from the Tijuana Toros, to the El Vergel Water Park and Mexican Lucha Libre.
The prices seem to vary, they say that you can organize a private trip which would cost $75 to $125 per person for groups of two to six, $55 to $105 for six to 14, and $45 to $95 for groups of 15 or more. If you are going on a trip they arranged, the prices may be cheaper. (The Lucha Libre trip on January 17 is $45).
Because the buses only have Mexican licences, you meet on the US side and cross walking, a faster way to come back to the US. But you should keep in mind that crossing to Mexico (crossing the bridge) is much faster than coming back (between 5 minutes and many hours).
The tours seem like a lot of fun and are definitely a great way to get your toes in the water. If you enjoyed your trip with the group and felt safe you can come back to Tijuana by yourself and get to know more of this fun city.