To get into Cambodia is real easy. Visa’s are now available at almost every entry point, whether you enter the country overland or by air. Note that visa’s for neighbouring Vietnam and Laos are not available at the border crossings.
For most nationalities there’s no need to apply for a visa at Cambodian embassies overseas. Generally that is much more expensive.
The visa process at the borders is easy and straightforward. Do not believe touts who claim you need their ‘assistance’.