The paperback is available from Amazon here for £17.99, although if you shop around you can often find it cheaper, such as at the following (although I'm sure other online retailers are available):
Wordery (currently £14.89 and free worldwide delivery);
Book Depository (currently full price but recently £14.00, and free worldwide delivery);
Hive (currently £12.95 and free home delivery, although they only deliver to the UK).
Don't worry if it says that it is out of stock. HarperVoyager are releasing it on a print-on-demand basis and some websites list these as "out of stock" or "not currently available" or something similar. However, this is just their terminology as they aren't sitting with copies in their warehouse and it can still be ordered as normal.
Watch out for delivery timescales - I'm not sure exactly how this works as it's new to me, but my understanding is that Book Depository is the quickest, especially for international orders (please note that this is based on the minimum of scanty research).
Anyway, I'm chuffed. I'm in print!