As might as everyone else on the earth, we have limitation of budget for the things that we always want and need - this apply for books too.
I try to look around for the best deals for book price. Tried out several retailers, Psychology Press (Psypress - which is a subs of T&F Book) - interesting they have different pricing scheme for the books that they sell.
Later I found out bookdepository. They sell book without shipping charges. But it is not always cheaper than let say, Amazon since sometimes the book price is higher than Amazon combined with the shipping fee. Last time I bought two books and it took more than a month (they refund me anyway). I still waiting for the other book from them since I bought a preordered book (yet to publish, at this time writing, I will be published in another two months.. given their track record I might only receive the book in the other three months?) Recently the put an offer for the already cheap books, for about 10% (this is quite a lot). I guess I will be convenient for you if you're already in UK, since it might be because of the cheap postage that caused the late book delivery.
Finally, Amazon. It's pretty convenient, of course the most trusted bookseller. I bought two books from Amazon on April 17 and just received the book on April 30, which is super cool. The packing is also very easy to open up so I am happy with Amazon. The price this time is cheaper than the previous bookseller so I am quite satisfied with their service.
Please tell your favorite!
By the way I found out this website which allows you to compare several book retailers so that it will be easier for you to decide which retailer you want to get a copy of your book.