My in-law’s performing a traditional Filipino dance in Japan and she wants her Filipiniana costume to be bought here. Where can I find a good one in Manila?

Divisoria has a lot of cheap Filipiniana dresses. I bought one there and I think I got ours for less than 2,000 pesos as far as I remember. You might want to rent, too. Try these sites: http://www.theprincessfashion.com/filipiniana-terno http://www.gownsforrent.asia/p/r/filipiniana-r/ Here's one of the the gowns for rent in The Princess Fashion Collection

Kultura in SM has a really good selection of Filipinianas. But if you want to save it's really best to go to Divisoria mall! :)