I was in HK when the Kabuto toys were released, and they were priced similarly to the JP retail price. As for after market prices, there is no real reason for a price difference between the BoA and BoJ releases, as they are identical.
I can only speculate that, since the BoA release came out about 2-3 years after the BoJ release, there may have been an after market price hike as it was the only way to get the toy because the BoJ one would have been out of production.