If you're only using it for the trip from the airport, buying a prepaid might be too much hassle. I do have a local sim card for PH, but whenever I've arrived in MNL out of balance or data, I've connected to the airport wifi (might be spotty at times) and booked a grab with that. Once the ride gets accepted, take down the license plate and move to the designated arrival bay.

That being said, the local sim cards are quite inexpensive. But Grab doesn't consume that much either, if you turn your mobile data off after booking.