it all really depends on what you are wanting to do? also if you are in the touristy areas off course it will be more. like bagio. I have livedi n the Philippines for years i did well on $500 usd a month. but then i live cheaply and adapted. it also depends on if you drink and do alot of the nightlife. I would say you will be safe with 500-1000 usd. if your white and in manila be careful cause taxis will offer you a drink or girl or whatever but who knows where you will end up. but then if that is what you want then just get in an taxi and he will take you to a bar and girls. Good luck. if in the cities be careful with the water in manila and cebu but other islands the water can be good i drink the water on negros and most visitors i know do also. try the street venders but then i usually do what the health department in america says not to with this. and remember you can bargain things down. even taxies at times will say no meter then try to get about 75% of what they ask. so you counter with just over half. that is what i do and i get great rates.
Really depends on what you plan on doing. Get an underclothes money belt from a sporting goods store & bring maybe $2,000 US (in $100 bills for best exchange rate) as you can always take back what you don't spend. The better hotels will have a safe to hold your money for you