Since been in divisoria 3x since august, here is the price of balloons/party supplies i've checked for the 1st birthday party theme:
9inches balloons 25 pcs: 75-80 pesos
12inches balloons 25 pcs: 100 pesos
buntings: 60 pesos per pack
party hats: 20 pesos for 12 pcs
Mylar balloons: 150 pesos per dozen
Pinata: 200 pesos to 250 pesos
hope this helps!