Don't know how many days a year you are spending in bkk on average? I managed to cut a deal with a fixed rate of 2780thb all year long with exception of the week from 23rd till 1st of Jan Bf and lounge included. I am spending average 30-40 nights a year in bkk
The lower rates at the Mercure didn't last long. The room I paid $78US a night for in late January has gone up to $102US. Better than the $125 they had been asking, but rates seem pretty fluid these days, thanks to dynamic pricing systems.