Simple, I have some already so not too much of a cost outlay.
Secondly it's because I love the Marauder minis of them. I have done for years, helped by the Dark Elf Warband in White Dwarf 144. The only reason I haven't truly pursued an army of the evil pointy ears is that they were one of the Armies Errny coveted also.
The problem with not collecting armies my dearest Brother collects is that it leaves precious few options. It was one of the big instigators behind my choice and continued devotion to Skaven. I have now decided though that not treading on my Siblings toes can no longer be a reason for not collecting an army of minis that makes me smile (a wicked dark smile).
I plan on this force fulfilling two functions, they will primarily be an allied force for my Skaven but they will also form the basis of a Slaaneshi army that will have the Beastmen and Thugs added to them that I painted as my Warband for the previous "Bring Out Your Lead" that I sadly never got around to using. Once I've dug these out from whichever box they reside in post move I'll post them up. For now here's the rest of what I have already.
As soon as the weather abates I'll get out into the garage and give this lot a spray undercoat and start painting. I also have one or two irons in the fire on Ebay for adding to this little lot.......................