If you're too late or too early for the bus, you can walk about half a mile into downtown Tijuana. Halfway between 3rd and 4th streets on Av. Madero, an alleyway holds the yellow-and-white station wagons that pack as many as 9 passengers on their way to Rosarito. You'll be more comfortable in the back (rumble seat), but you'll cringe every time a crazy driver tailgates you within inches. The back seat is the worst, that's where they try to cram in 4 passengers, but the fear factor is a lot less. The prices get higher as the night goes on, and I haven't been able to establish a pattern, possibly because the various drivers all have their own ideas on the subject. The 'tarifa oficial' is $11 pesos (1 dollar), but after dark it goes up to $12, then $20, then whatever the hell they want into the wee hours of the morning. Highest I've ever seen is $35, still only about $US3.20.
If you succumb to the gauntlet of tourist-taxi drivers at the border, you'll be paying from $10 to $15, or even more, for the same distance. Of course, you'll be more comfortable, and if you're traveling with a lot of luggage or with family, that may be the better choice. But for one person, the bus is by far the best deal, followed by the shared taxi.
Feel free to donate $1 to firstname.lastname@example.org for this money-saving travel tip.