sub select

Please help me!!!!!!

I have a table that holds products in a specified currency. I have set up three tables to convert currencies into two other currencies i,e pounds to euros and dollars, dollars to euros and pounds etc. How can I select all products and convert them to one currency type bearing in mind that the prices are arbitary numbers with a column that denotes what currency tyoe they are. I can select all products and multiply them by the figure in a conversion table delimiting results by the currency type column in the product table:

ie select product.price*euro_converter.pound_rate as Price_in_Euros
from product, euro_converter
where product.price like 'GBP'

The only thing that I can think off is to replicate this statement three times with a subselect statement but i don't know how to do this.