Unfortunately my attempts at price-fixing have come undone as far as the e-editions are concerned!
Due to the wanderings of the exchange rate, and the fact that e-books are subject to tax whereas paper ones are not, I cannot give a single permanent price for e-Books and Kindle editions. However they will always be around £3.10, though they will tend to go up and down a little.
Paperback prices are fixed at £6.00, which means that US readers may find them rising and falling in much the same way. Paperbacks which are larger than my standard A5 size will vary according to the book because they're individuals.