i will type this one out too.
U can get a one month visa(US20$ and one passport sized photo) on arrival at most land borders(except for those from Laos, and the Phnom Den/Tinh Bien Vietnam crossing) and Phnom Penh and Siem Reap airports. Getting your visa ahead of times will save u being overcharged at the land crossings. Also if you're planning an extended stay, get a one month business visa for US$25.
Visa extensions are granted in Phnom Penh. Tourist visas can be extended only once for a month, whereas business visas can be extended ad infinitum.
Officually an extension for one month costs US$30, three months US60, six months US$100 and one year US$150. However, the police will keep your passport for around 25 days. Strangely enough there's an express, next day service at inflated prices: one month US$39(for both tourist and business visas), three months US$80(only business visas) and so on. U will need one passport photo for the extension. Overstayers are charged US$5 per day a the point of exit.
Visit the new Immigration Office opposite Phnom Penh International Airport to arrange and extension
U can get the visa at the borders
u need one passport sized photo.
Tourist visas are valid for a single 30 day stay and enable u to enter and exit the country via any international border(make sure to specify this when arranging your visa). Depending on where u acquire it, prices for single entry tourist visas cost around US$30 to US$60. Cambodia, where your visa applicaiton can be processed on the same day, is the most convenient place in Southeast Asia to get a Vietnamese visa. Bangkok is another popular place, as many travel agents offer cheap packages including both an air ticket and a visa.
If u plan to spend more than a month in Vietnam or travel overland between Laos, Vietnam and Cambodia, it is possible to get a three month multiple entry visa. These are not available from Vietnamese embassies, but can be picked up for us$70 in Cambodia and for US$85 in the USA.
On the subject of visa extensions in Cambodia, yes they are done in Phnom Penh, but you don't necessarily have to to there. I had a travel agent in Siem Reap handle the whole process. Gave her my passport and the visa fee and 3 days later it was back in my hands and good to go. But that was using a Business visa. I would guess that a tourist visa is just as easy.
About Malaysia and Indonesia; I'm not sure about how safe it is or not. Usually the western media, and the always dire warnings issued by various embassies, exaggerate the danger of travelling to those countries. If you stuck to the well-beaten tourist path and aren't shouting anti-Islamic slogans you should be fine.
As for Myanmar, it's totally safe. And inexpensive and friendly. Despite its image as some sort of police state, that's far from the case. It's a beautiful and delightful country.
I'm doing pretty much the same trip as you next year, I'll be travelling for 8 months starting in januari in Myanmar. After that Thailand, Laos, Cambodia and Vietnam. But I am also including China and Tibet in my trip and my average monthly budget will be matching yours.
To me 1000 pounds for the flight ticket sounds a lot. I guess you live in the UK so if you haven't booked your flight yet you should check this site out. www.oasishongkong.com It's a new Hong Kong based company and you can get a returnticket for as little as 260 pounds incl taxes.
Hope you have a great trip, maybe I see you there!