The gateway to Bangkok is through international airport Suvarnabhumi, located southeast of the city centre in the Bang Phli district, Samut Prakan Province. Fly via Thai Airways International, Thailand’s flag carrier, which offers cheap flights to Bangkok on Economy and Premium Economy seats.
You may avail of promos, including a Discover Thailand fare package, which offers trips to 3 Thai cities for a small price; and Discover ASEAN fare package for those wishing to explore other ASEAN Member Countries. They also have a frequent-flier programme called Royal Orchid Holidays for both Economy and First Class fliers.
Another option for is Jetstar Asia, a budget international airline which is a subsidiary of Qantas Airways from Australia; they provide cheap Bangkok flights. Based in Singapore, the airline flies regional destinations within a 5-hour radius from Singapore Changi airport; flights can be booked online. The airline offers 20 kg baggage allowance, leather seats, and seating choices if you book online; you'll also fly on Airbus A320 planes, which seat up to 180 passengers.
Another airline to consider is Air Asia, Asia’s pioneer no-frills, budget airline which services the regional hub. It's currently offering its Go Holiday Travel packages to regional destinations, including Bangkok flights, alongside its Super Deals promo. Air Asia was the first to offer fully ticket-less travel on all of its flights in Asia. You get unassigned seats and only the necessities when you choose to fly Air Asia to Bangkok.