Tomorrow, May 1, is Labor Day, and, there's going to be seat sales for both Cebu Pacific and Air Philippines. Yay! Totoro-line wave!UPDATES:
Cebu Pacific's promo has a 90% off on the base price of their domestic and regcional flights. It means, the fuel surcharge remains the same. So, a roundtrip ticket to Incheon will still yield an almost Php 7,000.00 price. Promo period is from May 1 to May 2; travel period is from September 1 to December 15.
As for Air Philippines, their P1 fare refers to the base fare as well and it covers flights from Cebu and Clark, and Php 288 base fare for their Manila outbound flights. Promo period is from May 1 to 3; Travel period is from May 16 to July 31.
Cebu Pacific posted this teaser:
On the other hand, Air Philippines tweeted this:
Tomorrow = May P1. :)
— Airphil Express (@airphilexpress) April 30, 2012
So, it's possibly an 80% off from Cebu Pacific perhaps for flights until December or even beyond, and Php 1.00 base fare for Air Philippines' domestic flights. Most likely, both seat sales shall commence at 12 midnight. 
Good luck and happy travel planning! 