Help with cheap flight within Thailand?

Bangkok Airways owns the airport in Koh Samui and except for a couple of daily Thai Airways flights from BKK to Koh Samui has pretty much of a monopoly on that route. For such a short flight the prices are generally very high, check Bangkok Airways and Thai Airways websites to see if they offer any specials, July is the low season here and there's a good chance you might find a better price as you get closer to July. Otherwise you can fly to Surat Thani on Nok Air, Air Asia and others for much less and take a bus and ferry to Koh Samui and a taxi or car once you get there.