ebay is by far the cheapest, though, i must say. I got my 1250 army for about 120 i believe, including multiple great harlequins, 4 DJ's, a solitaire, and a shadowseer. 10 troupes retail is going to be aloooot more. If you want to go that route though check the australia section of the GW 40k store. i know they ship in the UK, havent checked the US as i did mine ebay, and had no reason to check the aus, but eh. I dont have any GW stores near me, as far as i'm aware of, so i havent considered that option.
GL.