ASEAN visa options for long-term stay in Cambodia?

You'll need a business visa and labor certificate, that's enough for a long stay.

To enter Cambodia, you'll need a different type of visa than the ASEAN tourist visa exemption. This can be obtained through the Cambodian government's e-visa website, ideally 2-3 weeks prior to arrival, or it can be acquired upon arrival. After obtaining the initial visa, it's recommended to visit a local visa agent to extend it before the 30-day entry visa expires. A 3-month extension, known as an EG extension, will give you sufficient time to work with an agent to secure a self-employed work permit. Once you have a work permit, you can then opt for a 6 or 12-month EB extension to further extend your stay.

We just go to HCMC Vietnam for a Visa Run, it costs around $150 and we get a longer visa. It's also a good opportunity to make a mini vacation.