Ok - I have your solution to this one. I live not too far away in San Diego and I am pretty well versed in this whole area. #1 Skip TJ. It sucks and it gives Mexico a very bad name.
1. Before you cross over the border, stop and get mexican Insurance. If you get in any kind of accident down there, they will throw you in Jail unless you can buy they guy a new car with cash on the spot and forget it if anyone is hurt. Mexican Insurance is less than $20. Do not skip this step
2. Cross over the border on the 5 going south at the San Yisedro border crossing. after you cross (usually no check going in to Mex) you will follow the road for about 1/3 to 1/2 mile and bear right then left to follow signs for Rosarita and Ensenada. You are looking for the Enensenada Scenic road (1). This whole tranaction will take 30-45 seconds and be pretty chaotic so just drive somewhat slow and keep your wits about you and eyes open. You don't want to miss this turn as the only well marked signs are on this road and getting back to this road is a crapshoot.
After about 5 miles (you will be drving along a sheet metal fence that is the US / Mexico Border going west) you will start heading down a hill. be ready to bear right to stay on 1 south and look for the toll road. Head toward Ensenada / Rosarito if in any doubt. After you pass the final exit for Rosarito, but just before you get to the next toll, you can (tolls are cheap and you can pay in US Dollars, just have small bills / change) exit and drive on a road that is parrallel to the toll road for the final 2-5 miles. You will know that you missed this exit if you pass by a large (the only one you will pass) gas station. It is okay if you miss this. There is an exit right at Puerto Neuvo. You just have to pay the extra toll for no reason. The village is on your right as you would expect and it is pretty well marked.
Your destination is a smallish fishing village south of Rosarito. The village has been built up over the years since Fox opened a studio there to film Titanic. The place is called Puerto Nuevo. It specializes in Lobster. Killer stuff here. You can get 6 lobsters with all the fixings and as much beer as you can drink for about $30-. Less if you are not drinking heavy.
There are lots of places to go once you are there. My favorite place is on the south end of town on the end of the second or third street. I like it because you can sit on the roof that overlooks the ocean. It is a little more authentic looking (read: seedy) but the food is great and the view is the best there is. Try to avoid the "nicer" places because your experience is less authentic. Ortegas is very popular. I would not go there becuause if you do this, you may as well have stayed in the US.
Be prepared for every vendor to bug you to eat with them. They are really selling it out there. Stay the course. You will know the resturant I am talking about when you see it. There are like ropes that are decorating the deck where you eat.
Try out this web site for some ideas if you want. If you like, you can PM me and I can help you with any other questions you might have.
Web site