I think you're looking for the adjective [**exorbitant**][1]: 

> (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.  


  [1]: https://en.oxforddictionaries.com/definition/exorbitant