Locking formula & copying

Hi

I have a list of countries attributed to rows with local currency in one column, exchange rate in another and then a load of other columns denoting variables (i.e. apples/oranges/bananas for example).

I'm using a simple formula to get the exchange rate =B13*$Z$13 where B13 is the variable (e.g. price of apples in Australia's local currency) and Z13 is the respective exchange rate to USD. When I drag the formula down to all of the countries, I don't need to lock either the country or the exchange rate however when I drag across the row (applying all fruits to the country) I need to lock the exchange rate as it applies to the same country.

At the moment I am locking the exchange rate cell, dragging across the variable row but having to manually change the exchange rate number cell as I go down the first column.

Is there any way to expedite this process?

Thanking you in advance,