The only hotel that connects directly to BKK is absurdly expensive. Try Rama Gardens. They have a shuttle, although you might have to take a taxi to get there. Just dig around at some bargain sites like passionasia.com or hotelclub.com. A lot of the places near the airport cater to the airline industry employees as well as business travelers, so they tend to be fairly well kept. Better 2 km away than down in the city center.