Try booking via the Bangkok Airways website — click on the logo below to go to it.
You might do a fare comparison with a site such as OneTravel, MakeMyTrip, or Utiket:
Hotel Thailand quotes some domestic Bangkok Airways fares that can be booked.
I found the current flight schedule timetable available on the Bangkok Airways website to be extremely difficult to navigate in Firefox, so I downloaded it to see if it functioned any more smoothly as the .pdf document it was designed to be. It can be negotiated much easier as a standalone document, I found; but it was 10.4 gigabytes as a download, and the full download took maybe four minutes to complete. I think they need to sacrifice on the richness of the graphics.
PB Air ATR 72-500 Bangkok to Nan Thailand
Uploaded by mach1video on May 12, 2009
PB Air 9Q-842, a Bangkok Airways wet-leased ATR 72-500 flies from Bangkok to Nan in Northern Thailand on April 12 2009. Good flight and very friendly cabin crew.