Plane tickets
Not sure where you are trying to fly in to. For Tijuana you just need to get tickets to San Diego and the drivers will pick you up at the airport and take you directly over the border to the hospital. They will do the same on the return trip. I generally use Orbitz or Sidestep but remember not all airlines are listed there. For instance Southwest Airlines is not associated with them and they usually have the lowest fares. I have also found differences in fares between what was on, lets say Orbitz, and what was on the airlines own website so you may want to check both.
Try www.kayak.com or www.orbitz..com I find my best deals on these two sites.
Good luck!