In case you really wanted it, the Burning Crusade Collector's Edition apparently isn't all that collected-- it's still in stock at Amazon for $74.99, a few bucks off the original price. The original Collector's Edition is a little harder to find-- it's been out of stock for a while, and copies are going for around $200. eBay is the same story-- you can buy the BC:CE for as little as $50, while the original CE is going for much, much more.
My guess is that it's the old laws of supply and demand-- by the time Burning Crusade dropped, everyone knew it would be a hit, so Blizzard made a bunch, while the original CE probably had a lot fewer copies made. But the noncombat pets might be a draw as well-- the original CE had Diablo, Zerg, and Panda pets, while the Burning Crusade only had a pretty unimpressive Netherwhelp pet.
And the other interesting question is what will happen when the next expansion drops. Being that WotLK is much more integral to the Warcraft that everyone knows and loves (while BC was much more involved with the ancient history of Warcraft), will people who've skipped Burning Crusade so far be more inclined to pick it up when Wrath releases? Maybe the BC:CE will get rarer as we get closer to Northrend.
[ via WoW Ladies ]