It looks like you could power the whole circuit from 2x1.5 V batteries?
The PIC16F628A can runn off 3 V, but your choice of the 16F88 makes me think that you need A/D too? I would suggest a PIC16F690 that can run off 2 V @ 10 MHz, is loaded with periphereals and is cheap too. Just a note: only the high nibble of PORTB is available (just in case you have to port old code...).
If you want to use an LDO regulator, you might consider the LM1086 (TO220, 1.5 A, but cheap and common) with 3 or 4 1.5V batteries [other options might be better].