Coûter la peau des fesses

Literally: To cost the skin off one's backside / the eyes out of one's head

Example: “Ce petit studio à Paris coûte la peau des fesses.” — That tiny studio apartment in Paris costs an arm and a leg.

English equivalent: To cost an arm and a leg

Origin: The series is unsettled, but one thing is certain: in the 19th century Alphonse Allais used simply coûter la peau, so at that point it was all of the skin that mattered, not the skin of any particular part. The fesses version is first attested only in 1976, in the Nouvel Observateur, though it was surely spoken earlier, and the cruder variants came after it. There is an oddity worth noticing: one of them uses the same anatomy as peau de balle, which means precisely nothing at all — the opposite. The eyes are a separate and older strand, found in Balzac among others in the 19th century, and the phrasing is strange in itself, since coûter les yeux would have done; the de la tête looks like reinforcement borrowed from expressions such as arracher les yeux de la tête. One story circulating online should be ignored: it has nothing to do with Ephesus and its bird whistles. The supposed appeau d'Éphèse is a pun and the appeau d'Écouilles behind the coarser variant is pure invention.