Baby clothes in the mall are so expensive. Where can I buy cute, quirky, and CHEAP onesies in Manila?

You may opt to buy online. Online clothes r usually cheaper and nicer too. You can try Qoo10, taobao.com, etc ... Some facebook users sell very nice clothes too and they are quite affordable. Alternatively, you can go to some groups in Facebook to exchange for those you need and bless those u don't.