prohibitively
Definitions
To a degree that prevents or forbids something from being done.
To an extent that is so high or extreme as to be unaffordable or impractical.
Examples
The cost of renovating the historic mansion proved to be prohibitively expensive for the small non-profit organization.
Due to the prohibitively high interest rates, many young families are currently unable to purchase their first home.
Synonyms
excessively exorbitantly extravagantly immoderately unreasonably