Here's how I see it..
-Last two expansions (TDB/HoW) $20 a piece =$40
-TTK {bigger than TDB/HoW combined} $40
...so pricing seems reasonable :)
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You forgot that they priced those class items and emotes at 20 extra dollars as well. So they consider a handful of cosmetics the same value as TDB or HOW. Seems about right.