We found the Ibis on the Accor hotels web site has been offering a room for 800 baht a night. It is pretty plain, but what a deal. They are in Ramkaenhang soi 7 or so, right beside The Mall (there are really two malls) with great parking and plenty of restaurants.
In the morning it is a straight shot to the new aiport on Rama IX.
Cannot remember the last time we paid 800 baht for a real hotel in Bangkok - this is about half their rack rate I think, perhaps even less than half. great deal