Phantom Liberty was always intended as a major expansion for Cyberpunk 2077. It's taken developer CD Projekt Red a long time to make (though in part because it spent months fixing the launch mess), but it's also looking like it's going to be bigger than a typical DLC.
That may be why the price of Phantom Liberty - if this leak is legit - is a little high.
According to Reddit user thebuffel, the price of the expansion was briefly visible on GOG.com, CD Projekt's own PC store. The user took a screenshot, and it's showing €30, which usually means $35 in the US.