Too add to the above replies:
How can you afford that? lot of saving up is true, but most importantly to be silly with money. SE.Asia is extremely cheap. You have gone there to experience a foreign culture, so don't go there to eat and sleep western. Western is expensive, and it is crap!
Your first few days might be more pricey than the rest as you get in to things and learn what is what.
Taxi's? True, ensure the meter is running. Unfortunately there will times where the guy will just look at you, and say tough ****, get out then. And the next 5 taxi's will be the same. It's all about supply and demand, if it's a busy Friday night, you leaving a popular spot, festivities - all these will lead to the taxi's or Tuk Tuk's charging more than usual. Learn what it would normally cost to get from A to B, add a few bucks on that, and you are good to go.
You will surprised by the cost of taxis, the same trip that would cost you £10 in the UK will cost you £2 in Asia.
I paid a guy £15 for the whole day to drive my around in Siem Reap Cambodia, I still over paid. But it is such little money if you take into consideration that's all he made for a day's work.
This leads to another point:
I understand that everyone says you must negotiate to get a better price. You will know when you getting ripped off or not. Please use your common sense and your heart when it comes to shopping. If someone sells you something worth a £5 back home for 50p, don't try get it down to 20p. You're not that poor, otherwise don't buy it, you clearly don't need it.
Clothes! Buy as you go along, fashion between backpackers is non existent. The more comfortable you are the cooler you look. The less you bring, the less you need carry.
Leave the jeans and hoodies at home. Bring 2x swimming costumes as you will most likely live 2 months on the beach in those alone.
Rule of thumb if you're on a budget, have enough clothes to last you 3 days, wear one,wash one, the other is in your bag.
Tip, leave lot's of space in your bag for the Russian market in Pnom Penh. Designer clothing at a fraction of the price. Original as well, as the factories are located there. The stuff will have a small defect hence the low prices. Top up on clothes over there and maybe post some home.
More advice - Learn the do's and don'ts, I see too many backpacker offending the locals because it is frowned upon in those countries. Locals will respect you more if you are considerate to their customs.
Be warned, you will fall in love with travel. 6 months will to short....a life time will be to short. Please make sure you make ever moment count, don't rush anything, enjoy the moment.