Did you completely ignore my first part of the message?
See if your country is on
this list - divide the cost ($5) by 100 and multiply by the number in that table, then convert the answer in the usual way to your own currency.
It's not perfect, but "technically" you may not be buying imported goods (certainly not in the EU, or anywhere there is a dedicated SCE subsidiary), so straight exchange rates aren't the best comparator.
EDIT: Don't forget sales tax; I don't think it's added for the US, because they do things differently per state, at least so I've read.
For the UK: the table says 133 (seems higher than normal, it's usually around 100), which translates to $6.65, which is £4.25 - plus 20% sales tax (VAT) is £5.10. So, in a sense (provided the parity of goods is applicable, and up to date) in the UK we're getting a bargain at £3.99! (Equivalent to $3.90 in the US). It's far from exact, and this is a massive over-simplification, but no more than straight conversion by means of a foreign exchange rate. Really, what dictates the price, as already said, is the value attributed to the market - i.e. how much they think we're willing / stupid enough to pay.