They go for that on eBay but I sold mine for about $30 I believe, which is a far more fair price. The decks aren't in that short of a supply nor is there that high of a demand for them.
What a deck is worth is up to you. If you look at the Pirate sets and think "this is what I need before anything else!" then they're probably worth more than $40 even! For me, I looked at them and thought "I would part with these in an instant if I was given $30" and I did.