Or you can find 36" of Kneadatite green stuff on EBay for $15...http://www.ebay.com.au/itm/Green-Stuff-Kneadatite-Blue-Yellow-Sculpt-36-Inches-/300645635406?pt=AU_Miniatures&hash=item45ffe0554e&_uhb=1#ht_2417wt_1139
Nice. Well there you go. the GW stuff is like 6" so that's about $120 worth at GW prices. I like the two seperate tubes as I find some of the greenstuff hardens in the centre if it's side by side ribbons.
Must admit the last pack of greenstuff I got was from The Warstore in the US, years ago... huge roll, still going strong...GW pricing... meh!
I sculpt and convert a fair bit, so I've gone through 2 sets of the GF9 tubes in the last year. I do tend to fill all the gaps I can and then use the GW liquid greenstuff to hide the seems and blend and texture.