This is a stupid question, having not been in a lot of other Tacomas. Without power locks, how are your rear doors locked? When you unlock drivers door, does turning it back a second time not unlock the other doors?
Going back to power locks, and assuming keyless remotes as an option.
On the '06, looks like all the door controls come out of the Body ECU, which looks to be above the drivers left knee. Since 2 of the 4 doors are identical, one under dash splice into existing wiring should cover those two. Power to a motor, reverses voltage to lock and unlock (2 wires).
For the front two, passenger has 5 wires going from ECU to the door, plus a ground. One of those goes to a detection switch, (code for door light switch I think)
Driver has 5 as well ( not the same 5 ) plus a ground.
The wireless receiver adds 3 more.
Might be easier and cleaner to talk to an alarm shop, ask how much to add an alarm and power locks at the same time.