i went to se asia last year for 4 months and i had a return ticket. for me it was perfect. but my friend decided to go home one month earlier so she changed the date of her return. of course she had to pay for it but it wasn't that much. the only problem was that she couldn't pay online and had to go to the office in bangkok.
it's cheaper to buy a return ticket, single tickets are soooo expensive. sometimes they are more expensive than return ones, i don't understand how it works..
Hi Joanna, the cost of the return ticket will depend on the type of airline you fly.
In the past, there were no low cost carriers (LCC) yet, so most international trips were booked roundtrip on the same carrier (that was the cheapest way). Unless one booked a full fare ticket (not discounted), where there were no or little restrictions (like non-rebookable, non-endorsable, non-reroutable, non-refundable, etc.). The endorsable part mean you could fly out of your destination on another airline, and with little or no charges to do so. The reroutable part meant you could change your routing (e.g. make a stopover, or even change the whole itinerary) provided the total mileage on the ticket did not exceed the maximum. And so on with the other restrictions, including doing such changes online.
When the LCCs (or even with discounted tickets) came, they dropped the fare quite low and slapped on most restrictions. At higher fare levels you might be able to rebook the ticket, but with a charge imposed. So it made sense to buy a one way ticket since if you had a roundtrip ticket that had the restriction of non-rebookability or re-routability, you'd end up paying more to change the itinerary. With two one way tickets, if you can't travel on your return sector, you'd just buy a new ticket (and throw away the original ticket you won't be using).
So now there are many LCCs in SEA, you can book these online and just bring a copy of your itinerary printout. This should be enough for the immigration officials as proof of onward travel.