For the record, the store demue is describing at Changi is attached to the very large duty-free liquor store in T2 between the E and F piers. All pax arrive and depart on the same level, so arrivals can purchase on the way in and departures can purchase on the way out-- just smoke 'em before you get back to the US. The cigar humidor is tucked away in the back of the wine section, which is to the left (when facing the store) of the liquor section and seems like a separate store. I seem to remember the prices as being steep but not totally out of line. I didn't buy, so I'm not sure, but the store may have done what many duty-free cigar merchants in Asia do: sell only by the full box of 25 or by the five-pack. If you're looking for just one or two, you may be out of luck.

The OP seems to be already out of luck for that store, since he's well-ensconced in his hotel.

Also for the record, the places I'd recommend in Bangkok are: 1) Bangkok Cigar Merchant (or something to that effect) on the bottom floor of Gaysorn Plaza, and 2) the Davidoff store on the main floor of, IIRC, the Peninsula Plaza mall on Ratchadamri (it's tucked away in a corner, so look around). The former, in Gaysorn, is bigger, has a wider selection, and plenty of comfy space to sit down and light one up. Prices are in line with the global market price. (If I'm wrong about the Davidoff store being in the Peninsula Plaza--which is nowhere near the Peninsula Hotel but is in fact next door to the Four Seasons--it's in the nearby Erawan Shopping Complex, but definitely facing Ratchadamri. I can't remember precisely because I can get there by feeling and usually go to the merchant in Gaysorn anyway.)