You might find one or two older manual lenses at Hidalgo, but you'll probably find that a lens you can get for USD $30-50 on eBay in the US, would probably be going for around USD $80-120 equivalent at Hidalgo.
For new Pentax lenses, your only brick and mortar choice is Camerahaus, which you can find in most major malls. And they are much (!) pricier vs US prices.
Henry's Photo once planned to bring in Pentax lenses, but that still hasn't happened, and it might not be happening at all.
Or you can try popular Pinoy versions of Craigslist (e.g. tipidpc.com), sometimes there are enterprising individuals who import lenses from Japan, and sell them online for a profit. They're cheaper than Camerhaus, yet they are
still more expensive than US prices.