I use Business Mail and am generally happy with it. You pay a yearly subscription, and then pay per piece for your mail - either sending or receiving.
As an example, I was out of the country for two months. When I returned my accumulated mail (I get perhaps a dozen or so letters a month) cost me 440 pesos in fees. However, the volume of mail was higher than usual.
Shipping packages works very well, but the shipping costs are higher. They have a service that gets the materials through Customs, which can be a headache otherwise. However, you never know exactly how much, or even if, customs will levy a fee. Business Mail does charge for the service in any case.