BUYING IN USD
On this website we quote book prices in UK pounds sterling (£ or GBP). However you can most likely use your USD or other currency credit or debit card to purchase our books. Your bank will pay Google Checkout, who handle our e-commerce payments, in pounds sterling, then debit you the appropriate amount in dollars. The appropriate amount will be the exchange rate at the time PLUS their charges which will probably add a few percent.
Given the current strength of the dollar relative to sterling and the fact that we offer FREE worldwide delivery even with the bank charges you should find purchase from this site reasonable.
Here are the current Google rates (BEFORE your bank charges) for the cost of some example GBP prices in USD:
(Some notes on Finding the best credit card for traveling abroad.)