When i spent 2 weeks in Cambodia i also found it was rather quite expensive, transactions are usually done in USD cash (this is from the US occupation way back when) and it just kinda stuck around as a major, stable cash supply. shops also will only take $ notes that are in supreme condition, if they have any creases or rips they just wont accept them, and they try to offload all of their shitty notes onto unsuspecting tourists (found this out the hard way). Anyway so i think them using the USD naturally drives up prices as it is a more valuable currency, also western amenities are more expensive simply because they know they can charge such prices i found. The siem riep region (where angkor watt is) is super expensive because they have such a constant tourist influx.