If it's for a one time thing, or for only a few parcels, Pos Laju would be the cheapest if I am not wrong. If it is to US, try checking out UPS.

If you would be sending in bulk/frequently every week or month, then you can contact EMS service operators like UPS, DHL, Fedex etc on their promotional/bulk packages. They will usually have cheaper than "retail" rates for those cases.