Carrier conversion cost depends on the carrier you want

How much would it cost to convert a ship to a carrier compared with building one from scratch?

A bare-bones escort carrier may be inexpensive to convert, while making a true modern carrier from another hull could cost more than building one properly.

Conversion cost depends on the desired capability. A minimal escort carrier can be produced relatively cheaply if operational expectations remain limited. Modern carrier aviation systems require major hull changes and high-end equipment. At that point, conversion can become more expensive and awkward than new construction.