Have you tried requesting to see if your carrier will let you unlock it? I've heard that at least with AT&T, they'll unlock iphones once they are out of contract. A co-worker came from the US recently and had his phone unlocked when he got here. The shop had to use a special unlock adapter that fits against the sim card. Maybe that's why the price they are quoting is so expensive. I think in LOS it costs about 500 baht or so for the kit and the unlock.