I was a really avid 1:6er up until a few months ago (not a lot on the market for my interests)
I can say that the price of Aliens related 1:6 stuff has been sky rocketing for the past year or two. The Hot Toys Marines can hardly be found for less than $400 a pop, with the exception of Drakes who I've seen resting on ebay at $375. To think that the Marines only cost about $85 at retail when they where first released. All that said it doesn't surprise me that something like the custom Newt (that isn't a barbie related doll) is going for so much.
I've seen Hicks and Hudson head sculpts go for $180, some times more.