The word going around is that 5th Edition is coming to an end this year. I lost my 5th Edition hardcover book a while ago and want to replace it. I was on Bartertown and found a quite a few people that could sell me a 5th Ed rule book for cheap. One guy had a collector's edition that I bought for $50. I think they sold for over a hundred back in the day but can't be sure. The only differences is that it has the fancy trifold cover, the purity seal (which is really just paper and a plastic seal) and silver-edged pages.
I wanted the book as a collector's item anyway. I am slowly filling my backlog of missing 3rd and 2nd Edition books. I also bought the old Angels of Death book for $25 in great condition. I also picked up the early 3rd Chaos Marine Codex for $10. The pieces are filling in like a freaky reverse game of Jenga but with books instead of wooden blocks.