For regional pricing you could fallback to the credit card location or whatever payment method they use, which in most cases includes a verified country of residence. This is specially import if you want to apply different VAT taxes depending on the location.

But even then this is still a UX problem because you don’t know the exact price to report until they have entered the payment information. You could try to guess the location and then change the price after entering the payment details, but it’s difficult to do this without coming across as being dodgy.

This gets even trickier if you take into account that different regions have different expectations about the inclusion of taxes in prices. It’s not only a matter of preference, many countries have strict rules about how to report prices.