Got an absolutely mint hardback copy of PJ Grant's latest edition book via Amazon at £25. There are a lot still about and there is also an American company that specialises in out of print books. Can't remember their name - something like ACD Books? - but they had 47 available, soft & hardback and earlier & later editions.
If you are interested in gulls I would suggest before you spend a lot of money on an i.d. book you spend a bit of time at a gull roost and get your eye in on all the different variations of plumage of the commoner species.Gull i.d is probably one of the most challenging aspects of birding,and there's no replacement for experience.There are plenty of articles on tinternet on gull i.d.(in fact Ian's preparing one at the moment with links to all the web sites).If like me you then get hooked on gulls,go out and buy the Helm book,its not perfect ,but its the best avaidable.But be warned,it can get very obsessive,good gulling.
It does indeed remain the best out there but it is not without it's flaws and reading it armed with little gull (no, not the actual Little Gull ) experience can complicate things considerably. For a beginner I still love the simplicity and general accuracy of Peter Grant's gulls book, an all time classic dealing with those species you're really likely to encounter and keeping it to the basics. Sure some things have moved on since Grant's book was last published and advances have been made but basics remain basics. Nothing though, and I do mean nothing, will assist you more than getting out and looking at them, whether you know what they are or not you'll soon start picking out differences in structure etc and then apply that to your reference material but don't run before you can walk, the ability to confidently and correctly seperate a 1st winter Lesser Black-backed Gull from Herring Gull should come before you attempt Yellow-legged and Caspian Gulls, if you know what I mean
Best hurry up and get my Yellow-legged Gull article out really which gives atleast a little advise on the basics of gulling.
Agree with Henry the Helm is a monster gull book, great plates with photos to accompany them. Only draw back is it can be very complex reading but to a novice like me learning it has all the info you could wish to need and more. Purchased from amazon for £31.99.
and correctly id them