Currency change for specific customers

At the moment the products_Results page and products_Detail page displays the product prices in pounds sterling, the numeric value in sterling is stored in the database and displayed next to a static £ symbol on these pages.

All the prices from thereon to the checkout page are conducted in sterling including all shipping and taxes.

Is it possible to distinguish when a user logs in to identify their country of origin based on their registration details and subsequent login to either display prices and conduct the purchase in sterling if they have registered with a UK address or to display Euros and conduct the purchase in Euros (including shipping and taxes) if they have registered with an address which is anywhere in the world outside of the UK.

There would be no automatic conversion for sterling to Euros but the client would enter fixed euros prices into the database for all the products (including shipping and taxes) and these would be periodically reviewed and amended when appropriate. These euro details would then be used for conducting the purchase for all users registered from outside the UK.

How would this impact on the backend of the site for inserting and updating product details and any other areas of the front end of the site?

I need to evaluate how big a task this is to respond to the client's request.