I did my TEFL in Vietnam (1 month course in Saigon) so i cant say much on where to do it here in Cambodia or how much it costs, but...
If you do have a TEFL minimum (uni degrees etc can help you out too) you've got a very reasonable chance of getting a job fairly quickly.
Experience is obviously better, but here in Phnom Penh if you get a job you're looking at about $10 for native speakers per hour, some schools pay the non-native speakers a dollar less or so sometimes, (dont forget you'll probably be taxed)
Receiving your salary varies from school to school, some are cash in hand every fortnight or month, some make you get a bank account or help you get one etc
Average working hours range from 7:30am until 11am with most, if not all schools having a siesta for 2 - 3 hours, school usually starts up again around 1:30pm until about 5pm, then you have evening classes which are very easy to get hours for as theres more demand for teachers around that time, usually from 5:30pm until about 8:30pm
A good way to do it is to go here http://www.eslbase.com/schools/cambodia
That link has a list of a lot of schools in Phnom Penh, but it's best to go directly to the main campuses if you can find them and leave a CV, Cover letter and a passport photo of yourself, you can also email them your CV and Cover letter as well, doing both obviously doubles up your chances.
I've gotten a job before where i had only emailed the school, not handed a CV in and got the job
(try to dress half respectively when handing in CV's, if you look like some greasy backpacker skank then your chances will slide)
A lot of schools arent on the same schedule either, as in terms here all seem to start at different times and last for different lengths, a term is roughly about 3 months long though, so ive found when it comes to hiring they do it more at the end of the term/just before the new term.
Another thing to remember is that some schools after the final exams will have a term break, this can be a couple of days or it can be a couple of weeks, AND like all the other holidays you get here, it'll more than likely be unpaid.
Here in Cambodia there are a lot of holidays that are unpaid with most schools, you also wont get paid for sick days either, there are some schools that have different policies, but usually not being paid for holidays and sick days is the case with most.
Good luck, dress smart for the interview, clean shirt, a tie, pair of trousers, decent looking shoes, try not to be too hung over or blazed out of your mind.
Ask questions like whether they help with visa extensions? do you have to write the exams yourself? how much is the tax? how much notice do they expect if you want to quit?
One school i worked at took $100 from your wages ($25 for your 1st 4 paycheques) i guess in case you decided that you want to do a runner half way through the term, they have $100 of your lovely, hard earned cash to deter you from doing so, its even worth trying to negotiate for a buck or 2 more, if you dont ask you dont get.
Average hours are about 25 to 30 hours a week, if you're lucky and theres no holidays, a normal salary will be around $1000 a month.