Something very old could be primeval (earliest, first) or primordial (oldest).
The term is exorbitant. Something with a high price is called expensive.
To recover something, or to retrieve it.
Alternate. substitute (verb)
It means to replace something, with something else that is equivalent.
The likely word sought is substitute (something used in the place of something else, or an alternate player in sports).
The word that works is idiot.
The word "ancient" is an adjective applied to something from a comparatively long time ago. It can be used to mean "very old."Historically, it describes a period of antiquity before the Middle Ages. But it can also be used, metaphorically, for anything archaic or outdated (e.g. his ancient computer could not run the program).
The word substitute can be a verb and a noun. The verb form means to use something in place of something else. The noun form is a replacement for something which does a similar thing.
Something that is lost and then found is recovered.
The adjective is indivisible.
Synonyms include flawless or ideal.
Ancient