I was mostly comparing against 4 star hotels in the same locations, relatively central and close to transit. They were typically around the ~$80 range. Add in taxes etc and you're looking at ~$100 per night. Airbnbs in luxury condos with some discounts (early bird, longer stay) you can get for ~$40 per night. So not quite 1/3 I guess.

EDIT: Luxury condos in Bangkok I find to be very nice. Last one I stayed at had gym, roof top infinity pool, movie theatre, library etc. And it was a few minutes to the MRT.