George,
I would not worry about the battery life.

I am working on a system just by chance using the same PIC and transmitter. My application is what I call a laser fence. The PIC with the transmitter has a photo diode looking for a 10 Hz pulse, if any thing other than the 10 Hz pulse is detected the transmitter will then transmit. While the pulse is correct there is a LED blinking, when the beam is broken or not the correct pulse the LED will be on continuous.

The whole thing is running at 3 volts or less on batteries. Four AA rechargeable.(series / parallel ) The PIC is running a 4 MHz external, never goes to sleep. The transmitter VCC going to LADJ and PDN pins all of the time.

I too was wanting to know how long the batteries would last as this will be remote and on solar when complete. About three weeks ago I started my test with out the solar with hopes that it would all run for two or three days on a charge. As I write this there is still 2.21 volts in the batteries. At full charge the NMH batteries had 2.6 volts.

I know this does not answer your question, but do not worry about powering the PDN pin from the PIC. I got three weeks plus with four batteries, that should work out to 1.5 weeks plus with two batteries.

The answer to your question would be a low gate voltage P channel mosfet. Fairchild should have one but I do not know the part number. I know their FDB7042L N channel works well at these voltages.