I've found a great ebay seller who is selling packs of 10 Euro up to 20gram/Worldwide up to 10gram,
or 10 Worldwide up to 20gram stamps for £9 on ebay.co.uk. This price includes free 1st class P&P.

These are perfect, brand new, post and go stamps, legal for postage, and they offer you a good saving compared with prices of these stamps from Post Offices. Just in time for February InCoWriMo.

No affiliation with the seller, just a happy customer.