Over the years I have bought various bits and pieces from Deal Extreme who ship around the world from China.
Recently I realised they have a Gardening Supplies section with various garden tools and gadgets. Among the items there was Mini Garden Nylon Grass Trimmer Line – Light Purple (15m) at £4.07 (6.50 US$) as seen here with free international shipping, this is 2mm trimmer line.
I wondered how this compared to buying locally. Screwfix are currently offering 15m packs of 2mm nylon trimmer line at £4.99 so based on this it would be cheaper to get it shipped half way across the world rather than buy locally! On they other hand they are offering 126m packs of Professional 2mm Nylon Line for £9.99 so I guess it pays to buy in bulk.
If you cannot justify buying over a hundred metres of nylon line the best deals on shorter lengths, such as 15m, were on Ebay.co.uk.