[Fiction question] What was the cost of a bowl of noodles in a Phnom Penh market in 1973?

Here is a picture of a 1000-riel note in use in Cambodia in 1973. That spring the American troops were to withdraw; two years later, the Khmer Rouge would advance on the city and evacuate all the inhabitants, launching one of the worst acts of genocide in history.

For a little while between 1973 and 1975, something resembling normal life went on in Cambodia’s capital.

How much would a bowl of noodles at an open market stall have cost in riels in 1973?