Pop-up Books tend to be expensive due to the complexity of manufacturing them - a lot of the work is still done by hand. But there ways of starting a collection on a budget.
E-BAY is a great source of used pop-up books. On the search enter "pop-ups" and/or "popups" and search the books section. Check the whole listings first before placing a bid - it is VERY annoying to bid on a book only to find it much cheaper a few books further on.Decide the maximum that you are prepared to pay (including the postage) and off you go.Do me a favour though,if the current bidder is 'popupz' it's me - I'll say no more.
WARNING! I have just purchased my second book from 'syntax64'. Both were described as good condition - both had damaged pop-ups, torn off pieces and generally disgusting condition. Avoid this seller like the plague.
THE WORKS are a series of discount bookshops throughout the UK. They usually keep a number of pop-up books in stock and stocks do seem to change quite regularly. Their web-site gives details of local branches.
THE BOOK PEOPLE are an excellent mail order bookseller. They are not a club, you order just what you want, and price are VERY low. If you order enough they will give you free postage.
BIBLIOPHILE BOOKS are another postal supplier who regularly send an interesting and quirky 'newspaper' full of unusual books free of charge. If you prefer to cut to the chase it is better to search their web-site for 'pop-up'. But you will be missing a gem of a catalogue.
There is a web-site specialising in finding the cheapest price for books.Known as FETCHBOOK it deals in new and used books.The UK site has recently been 'consolidated' into the main site and now has a heavy American bias. Worth a look though.
Sometimes the publishers themselves have special offers.HAWCOCK BOOKS have had an offer on 'Pop-up Stand-out Dinasaurs at £4.99 instead of £12.99.
Their are also a number of book fairs around the country. These range from the local village halls to massive fairs such as Chelsea, Edinburgh and at Haydock Park Racecourse. To find your local one check outThe Book Guide and the PBFA. I must also give a plug for my local fair at the Pavilion Gardens, Buxton.