August is school holidays so always more expensive but its not the best time to fly to Thailand as it will be rainy season. Ive been twice and the cheapest is aeroflot the russian airline but it is really bad service etc and there is a stop in Moscow for a couple of hours but I paid each time about �350 but I went in April and May - when I went you had to phone to book them as well and not able to do it on line that may have changed - they have an office in Green Park in London