Velkommen guesthouse
Here's where we stay, USD16 per night, breakfast not included. The room is not big but clean and comfortable. This guesthouse is near to riverside, walking distance. Lots of restaurant/cafe/shop lots around. Warm welcome and friendly staff here. Stay in Cambodia (our experience), we no need to pay for deposit and accommodation fee when we check in, there will only bill to you when check out (this make me feel more friendly, is not about money and money). We got lots of information likes tour, transport, and also we bought the van ticket to Siem Remp through the guesthouse. Opposite the guesthouse is Velkommen backpacker, dorm room and offer cheaper price.
Find out more at: http://www.velkommenguesthouse.com/
We had breakfast at the guesthouse (not included) before we heading to Siem Reap (approximate 6 hours). There's western style breakfast such as scramble eggs, toast.... available here.
The stay in Phnom Penh in not expensive. The average price is USD15 for 2 person stay in guesthouse. You can easily find the accommodations (hotels, guesthouse, backpacker dorm) at the areas along the riverside.