I think you're looking for the adjective exorbitant:
(of a price or amount charged) unreasonably high.
‘some hotels charge exorbitant rates for phone calls’
And yes, it specifically means unreasonable, but not necessarily unaffordable. In the example sentence I've quoted from the Oxford dictionary, a hotel guest can probably afford to pay a high rate for a phone call, but they find the amount unreasonably high.