The same value can cost a different amount in USD depending on the region. Here is why.
A 20 GBP card and a 20 EUR card are not the same price, because the currencies are different. Even cards in the same currency can cost a little more or less depending on the region.
What matters is not the cheapest region, but the one that matches your account. A cheap card that does not redeem on your account is not a saving.
Compare the USD price on JR with what you will get in your account currency, and choose your own region.