us-east-1 and us-west-2 pricing is locked to each other. Typically the power differences are related to the cost of power and transit/peering, not the capital of building the facilities.

Northern Virginia and Oregon have (generally) cheap power and cheap connectivity to anywhere in the world, with plenty of peering opportunities. In a developing country or with more expensive infrastructure (Mumbai, Tokyo) costs will be higher to get power and pull in fiber to peering locations with enough capacity to supply a provider of Amazon's size.