Just to add to jmeangel's answer.
Basically, the NAV can be determined by the fund, i.e.
it can start at 1,10,100,1000. I haven't seen a fund with
a NAV that started at 10,000 yet haha.
The rest of what jmeangel said basically boils down to performance.
And a NAV of 1 is not "cheaper" compared to a NAV of 10.
What matters is how fast the NAV go up

Try to calculate it.
If you had 1,000 pesos and Sunlife's NAV was at 1.
You get 1,000 shares.
Now a year later, Sunlife's NAV is 2
Your 1,000 shares is now worth 2,000 (1000x2)
If you invested the same 1,000 pesos in BPI and its NAV
was at 100, you get 10 shares.
Now a year later, BPI's NAV is now 200.
Your 10 shares is also worth 2,000(10x200)
See, no difference. What matters is the ending NAV

Now with that said, to really answer your question about
why BPI's NAV is like that. Its because its probably the
worst performing equity fund around hahaha :p
Seriously