I'm told there's an offer in the Radio Times - 20 free 'in the green' snowdrop plants. You pay only £3.71 p&p. Apparently you go to www.plantoffers.com and type in RA142 in the code window.
(Haven't done it myself yet so I hope it works!)
Just had a look. http://www.plantoffers.com/az.html (http://www.plantoffers.com/az.html) They seem to have other postage only offers too.