I call your BS,
Cambodia is from the three countries you mentioned still the cheapest, maybe the beer in Vietnam is cheaper when you go to a local Bia Hoi corner.
Accommodations, food and drinks are in Cambodia the lowest of SE Asia except Laos I think.
Tell me where can you find $1 GT's or beer in LOS/Vietnam (brand name no Bia Hoi)? I prefer my drinks in a bar or restaurant not in front of the 7-11. I also sleep in hotels not hostels.
About ripping off tourists Thailand is absolute King followed by Vietnam, Cambodia is a quick learner.
Here is a Wise lesson: I transfer at lowest possible fee (1.5%) with the highest rate, my Euro's into Baht to my Kasikorn account. My K-card is not charged any fee at the ATM when collecting cash. With my Wise wallet in my phone I can pay at any store in SE Asia.
Filling my debit card wallet via Wise in any local currency (Baht/Dong) is even a cheaper fee (0.67%) with the highest rate compared to all the system banks.
Oh and BTW you can have a Happy Pizza just for $4 in PP, please try makes you more relaxed.