I have to be honest here, I'd be hesitant to recommend anything to you. Absolutely no offence intended but I always am for someone who - as you yourself indicate - has little experience with bikes (especially here in Thailand). What with that factored into the road conditions and sheer insanity of other dirvers at times it makes me uneasy.
That being said, and from what you've said, I'd say a CBR400 would be your best bet to fit all the criteria you have given. They're big enough to comfortably ride distances, but not so big that you'd have a lot of trouble handling it. Also they're relatively common so parts/servicing wouldn't be an issue. You could probably pick up a good one for around the 60k mark fully registered, 40-50k for unregistered.
Just make sure you spend a goodly amount of time getting used to and comfortable with it before you take any trips. I apologise in advance if any of this sounds patronising but I've riden bikes my whole life and even I'm not so keen on it here anymore.
Here's a pic in case you were wondering:
