Wiktionary
vb. (context idiomatic English) to be a huge expense
Usage examples of "cost the earth".
Peddlers, and even merchants, sometimes brought brandy or ale from outside, but it was never as good and cost the earth, besides, and nobody ever drank it more than once.
The kind that came in gorgeous bottles, cost the earth and made a woman feel like a queen.
That original appellation was before my time, and I confess to a degree of yearning for an age when bars had, in the main, sensible names, and did not pride themselves on serving their own creakingly-titled cocktails, a Choyce Selection of Our Eftim-able Home-Made Pies, Hotpottes And Other Fyne Dishes, and twenty different designer lagers, all of which taste identical, cost the earth and are advertised on the tellingly desperate Unique Selling Points of having a neat logo, a top that is difficult to open or a bottle neck whose appearance is apparently mysteriously enhanced by having a slice of citrus fruit rammed down it.
And the plain velvet curtains had probably cost the earth but the colours were drab and boring, and so were the settees and chairs.