Thailand forum

There are very few actual "hostels" in Thailand. Budget accommodation is typically in a "guesthouse" and there are tons of them in the Banglamphu area near the river (Khao San Road, Soi Rambutri). Most of the cheapies can't even be booked in advance, but you might check out a site like http://www.hostelworld.com or http://www.hostelbookers.com (which will list guesthouses too). If you're coming in on a long flight and are unfamiliar with Bangkok then it's not a bad idea to at least book the first couple nights then look around for something cheaper. Also look at the listings right here on Travelfish.

From the airport go to the metered taxi rank outside and tell them you want to go to Khao San Road, make sure the driver turns on the meter, and then it should cost about 400 baht. Depending on time of day there can be some gridlock traffic around 5-7pm and it can take an hour or more - it's pretty far. You could alternatively take the Airport Rail Link but it doesn't go to that area and could get more complicated. It's good to have notes smaller than 1000 baht too, as taxi drivers are notorious for not having change (yeah right).

If you're curious about scams check this out
http://www.bangkokscams.com

Just as the others have recommended, I typically only book accommodation ahead of time if I'm arriving in a large city that is new to me or expect to arrive late at night. Otherwise, it is fun to just turn up and see what looks good at the moment. I'll typically have two or three places in mind from my research, like reading the reviews on TF, to use as a price and quality guide. It is easier to check out more places if you are travelling light and don't have a huge pack to lug around. The only other time I book ahead is if there is a particular place I want to stay.

As for getting into town, the metered taxi is your best option, particularly since they give you a receipt at the taxi line with the license plate number on it. They'll use the meter plus an airport surcharge of 50 baht or so plus tolls. But even then, as Bob-0 says, it is only about 400 baht, which is an absolute steal compared to most other places.

Finally, I've done my fair share of hostels, but in Thailand rooms tend to be pretty affordable, and you can get your own room with air con and private bath and even cable TV with english channels for less than you'd pay for just a bunk in Oz or the states. Rooms will get even cheaper as you get away from Bangkok. And although Captain Bob is too polite to mention it, he runs a guest house in Chiang Mai with rooms with shared and private bath options at very backpacker-friendly prices. Cheers.