Phnom Penh Travel Forum

Hello, everyone, I would like to ask you about money matters staying in Phnom Penh for a longer time. I am doing my Masters in International Development and I specialize on SE Asia, particularly Cambodia. At the end of July I am coming to Phnome Penh to undertake a 4-month unpaid placement at one of many NGOs there. My question would be how much money do I need to have a descent (not posh) life in Phom Penh. Is 500-700 $ a resonable amount of money?
I have been to Phnom Penh before as a tourist, but I can't make any conclusions just spending there two days. How much is a regular room to rent in nowadays and how much would I need for other expenses (food, entertainment, etc.)?

Best regards,
Paulius