Aquabid.com is my favorite place to buy...well...anything.
I just bought 6 ABN's that arrived today, and the seller sent me 8 instead, all alive and expertly packed ($25.44 including shipping).
When you think about it, ordering a fish online isn't any different from how the bettas get to the fish store. They're shipped in insulated, padded boxes with heat packs for warmth.
If you want to order one, I'd recommend looking for a breeder in the states as opposed to in Asia, that way they'll arrive a LOT faster. No cross-world flights and sitting is customs. I always try to buy local bred fish whenever possible, no matter what kind.