Which is about as jaw-dropping as what people spend on WoW and other pay-to-play games to get to the end game.
(Even more incidentally, I am pretty sure you can get to WoW's end-game within a couple of years of playing, so $150–$300 seems like a reasonable estimate of that game's TCO.)
Some of the Naxx cards are definitely cool, but, like all the other cool cards, none of them make or break the game. Sure, Sludge Belcher is the best taunter in the game right now, but it's only slightly better than the Sen'jin Shieldmasta, which is still a fantastic card and is still absolutely free.
Access to good cards is helpful, but nowhere near as important as strategy and experience. Heck, go watch some of those free-to-play folks who start fresh accounts, never pay money, and still rank waaay up. If you refuse to concede when things look bad, you might be surprised by how well you do.
(Also, the Naxx single-player content is excellent. Even if you choose not the use the rewards, Naxx itself might still be worth the price.)
(It's just 'Hearthstone' by the way.)
My estimate is slightly lower ~350 packs, but I had to guess a lot of numbers.
