If you want to save power you should get rid off the 78L05 and use a better one.

You could also run your pic straight from 3 AA cells in series(4.5V), the pic consumes only a few uA at 32kHz. The AA cells should last a few years. 32kHz should be enough for beeping and counting time.

Your project would then be reduced to.....

1 Pic
2 capacitors(for the crystal)
1 32kHz crystal
3 AA cells
1 button
1 beeper

..... if you accept a bigger timeerror you could get rid off the crystal and use the builtin oscillator of the pic. The 16F627/8 has a 37kHz(ish) oscillator, the more modern pics with nanowatt should be even better. Using one of theese would reduce the project even further....

1 Pic
3 AA cells
1 button
1 beeper

... it won't get much simpler than that.

/Ingvar