Accommodation in Cambodia is cheap, in general. During the low season, it is even possible to secure free lodging at some of the guesthouses on Serendipity Beach in Sihanoukville, in exchange for eating meals there. In general, a decent guesthouse with private bathroom won’t cost more than $5-$6 anywhere in Cambodia.
A bare-minimum, filthy room with shared bathroom usually costs around $3. Camping in Cambodia is not much of an option, unless in national parks or remote areas, and these areas are difficult to find and generally avoided because of the landmine risk.
Khmer food is a huge disappointment. It’s as sloppy, badly made, and unhealthy as just about everything else in the country. One huge complaint is that it’s full of small bones, particularly shards of chicken bones that stab into your stomach and scratch your throat if you don’t dig in and just eat with your hands. In general, it’s the worst food in the region.
There are a few good dishes, though, if you can find a decent cook. One is Amok, a sweet and spicy coconut curry served with rice. Chicken with hot basil is quite tasty as well, but usually served with so many bones as to be inedible. Char Lok Lak is decent, but a very basic meal of fried meat in oyster sauce served on raw onions with a side of rice.
Otherwise, there is good Indian food in Phnom Penh, especially, and other western restaurants, though they are more expensive. In general, street food is better avoided, though hot foods like fried rice are a possibility. Don’t expect much.
A local meal usually costs around $1.50-2.50, though prices are rapidly going up. Western food, especially anything with cheese, milk, wheat flour or other imported products, is very expensive. A medium pizza costs around $8 and up (a week’s wage for a local). In general, eating in Cambodia is more expensive and less appetizing than in neighboring countries.