Hey, my piece of advice:
1) If your phone uses a SIM card, get it unlocked, or better yet, if it's already unlocked good for you. That way, you can get a SIM card at any Oramge dealer for 350 pesos with 100 pesos of airtime. If you cannot use the phoen from home, you'd need to buy one. The cheapiest junkie phone would cost you about 1000 pesos.
I see an offer of Benq Siemens A70 at 590 pesos with the orange card program (prepaid) don't know if that includes the 350 card activation or it's on top of the phone price.
Orange ™
2) You can buy a refurbished Verizon (CLARO) CDMA phone on the streat or any Verizon/Claro dealer. You would pay anywhere between 500-3000 pesos depending on the model, functionality, color screen, camera, video recorder, etc. Comes with airtime of anywhere 200 to 300 pesos. I have even seen offers where they sell you a phone at 300 pesos (junk, big phone from 90's) at 300 pesos with 300 pesos of airtime.