It is possible to display a second currency for standard product prices (within 'Business Settings | Options') but these dual currencies do not show for prices within drop down lists by default.

It's possible to do this with the following fix:

First of all create a new variable (via 'Design | Library | Variables') called 'EuroRate'. This variable needs to have a 'Place of Setting' of 'Site' and also needs to have a 'Type' of 'Number'. For more details on creating variables, look at the main help in Actinic under 'Understanding Variables'.

Then set a value of 'EuroRate' within 'Settings | Site Options' of whatever you want your exchange rate to be.

Finally go to 'Design | Library | Layouts' and find the 'Permutation Prices' group in the library. Edit the 'Additional Price in Brackets' layout and replace the whole of the layout with the following code:

<actinic:block if="%3cactinic%3avariable%20name%3d%22PermutationAssociatedPricesAreUsed%22%20%2f%3e%20%3d%3d%20FALSE" >
( <actinic:block PHP='true' SELECTABLE='false'>
formattedcurrency(<actinic:variable name="PermutationPriceRaw" />, <actinic:variable name="CurrencyDigits" />, '<actinic:variable name="MoneyDecimalSeparator" />', '<actinic:variable name="MoneyThousandSeparator" />', '<actinic:variable name="DefaultCurrency" />');
formattedcurrency(<actinic:variable name="PermutationPriceRaw" /> * <actinic:variable name="EuroRate" />, <actinic:variable name="CurrencyDigits" />, '<actinic:variable name="MoneyDecimalSeparator" />', '<actinic:variable name="MoneyThousandSeparator" />', ' %u20AC');
</actinic:block>)
</actinic:block>
<actinic:block if="%3cactinic%3avariable%20name%3d%22PermutationAssociatedPricesAreUsed%22%20%2f%3e" />
( <actinic:block PHP='true' SELECTABLE='false'>
formattedcurrency(<actinic:variable name="AssociatedProduct::ProductPriceRaw" />, <actinic:variable name="CurrencyDigits" />, '<actinic:variable name="MoneyDecimalSeparator" />', '<actinic:variable name="MoneyThousandSeparator" />', '<actinic:variable name="DefaultCurrency" />');
formattedcurrency(<actinic:variable name="AssociatedProduct::ProductPriceRaw" /> * <actinic:variable name="EuroRate" />, <actinic:variable name="CurrencyDigits" />, '<actinic:variable name="MoneyDecimalSeparator" />', '<actinic:variable name="MoneyThousandSeparator" />', ' %u20AC');
</actinic:block>)
</actinic:block>


You can now click 'OK' on the layout and check your preview.

Thanks to Norman Rouxel at DrillPine (http://www.drillpine.biz/) for this solution.