Here is a price list in Cambodia for reference (by 2015):
A bottle of water (500ml): US$ 0.3
A local beer at a bar/restaurants: US$ 1
A glass of coca cola in a restaurant: US$ 0.7
Average price of street food: US$ 1
Western decent meal at local restaurant: US$10
The official currency in Cambodia is the Cambodian riel, and US dollar is like the second official currency. This means is that you don’t need to be concerned about getting riel when you arrive in Cambodia. You will pay for the Visa on Arrival in US dollar. Tourist-oriented businesses and stores quote price in US dollar. Even for price marked in riel, you can pay in US dollar. Because they don’t use American coins in Cambodia, you’ll get change for your purchases in riel.
If you do want to change money so that you have riel on hand, you can do so at banks or in local markets. It’s rare to find notes over 10,000 or 20,000 riel ($2.50 and $5, respectively), so changing a relatively small amount of US dollars can leave you with a big pile of cash.
ATMs in Cambodia dispense US dollar. You may contact your bank for detail instructions of daily withdrawal limit and charge. Small notes will be very useful for tipping and local street shopping. If you are going to bring cash to Cambodia, please make sure notes are in pristine condition with no defects, or they will likely be rejected as counterfeit. Get the most recently dated notes you can as these stand the highest chance of being accepted.
As to tour cost, you may compare