Hello,
I'm new into comic collection.
I don't know if this is usual in the comic industry about prices going up within a few months time after their release, but recently I've been noticing a sharp increase in price (of collected editions, that initially, at the time of their release) costed much less.

I mean the Omnibuses/TPBs/Collected Editions that released 6-8 months ago on Amazon, whose prices initially ranged from 20 to 50 dollars, now after 6-8 months their price actually ranges from 80 dollars to 135 dollars. Some even go as high as 200 dollars or more.
... And some of these brand new collected editions even become unavailable on Amazon, only to become available later (as used copies) from sellers with bad ratings.

Is this a known thing among comic fans? Does the price goes up all of a sudden just a few months after their release?