FB is right about the Thai logic as to recouping loss - I stayed in Lai Thai a few weeks ago and, though I got two rooms for 1100 Baht, it was not as good a deal as I have been able to make previously. Actually its also what the British Govt did with the Millenium Dome, not enough people were turning up (due to bad press), so they put the price up!

As to renting for 4 months, its doable I guess, but most want at least 6 months. As FB suggests, you may be able to make a deal with a guest house hat works out as cheap for easier (and have the benefit of room service!). Do you have any Thai friends here that can help make a deal for you before you arrive?