Quote Originally Posted by Mancs
And the cheapest way is to get the slower train from the lower level of the airport to Makkasan station (30 baht or so), exit from there and cross the railway line to Phetchaburi underground station, then get the tube train just a few stops to Lumphini station (maybe 25 baht). The hotel is ten minutes walk from there.
There are Express Line and City Line. The latter stops at all stations, is therefore slower, but cheaper. There is no direct connection from Makkasan to Phetchaburi, it's about 500 meters walk, not recommended if you have luggage.

With local knowledge, you might be able to find a bus connection that is a few baht cheaper.