FYI: I used Uber on my last trip to BKK. While I was collecting my luggage there were 3-4 cars waiting. When I exited the customs hall, I snagged the last car. Flat rate 1000 to Sukhumvit.
I also used Uber to transit from my Sukhumvit hotel out to the new LeMeridien Golf resort near the airport. It was 660 or so.
Unfortunately there were no cars within rage for my LM->airport transfer so I needed to call a cab.