I live and Los Angeles and my dive buddy and I drove to the Bay of Los Angeles in Baha Mexico which is on the east side. It is about 400 south to Tijauna. The spear fishing and diving was great. There is one place to get fills and the cost's $10 each. We hired a guy with a small boat to take us out at $135 per day.
We tried to get fishing liscenses in a US border town before crossing into Mexico but were told. You don't need not &*$#* fishing liscenes in Mexico. We got the same response from our boat captain.
If you drive to through Baja heres my advice.
Don't do it at night. We did and it was a mistake. The one road is very small and windy. We saw at least 8 cars smashed on the side of the road. There are also road side memorials everywhere. We drove back during the day and it was great. Baja is beautiful place, except for the multitude of dead dogs and cows that are on the roadside.
You go through numerous Federally Road blocks. Sometimes they wave you through and sometimes they don't. I would not want to get busted for drinking or pot down there.
To get to the Bay of Los Angeles you have to get off the main road and drive 40 miles east. The first 20 miles is a newly paved road which is great. The last 20 miles is the worst road I have ever been on. You need a 4 wheeler, truck or SUV. The town has about 400 people and there are a few small hotels which are decent. The rooms are about $35 a night, meals are $3-$5 each. There are a couple of stores that sell everything from beer to shovels. You can buy gas from a guy who keeps it in a 50 gallon drum. The hotel owner can hook you up with a boat which is bascially one guy and 15 foot boat.
The diving there was great. We had the entire ocean to ourselves. We saw at least 20 whales and huge schools of dophlins. We shot some grouper and El Dorado. There is a place where they do research on Sea Turtles and you can help clean them.
This link has some good maps of Mexico and Baja.
http://www.maps-of-mexico.com/