Proper cost confused one looking for something precious (10)
I believe the answer is:
prospector
'one looking for something precious' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'proper cost confused' is the wordplay.
'confused' indicates an anagram.
'proper'+'cost'='propercost'
'propercost' anagrammed gives 'PROSPECTOR'.
Can you help me to learn more?
(Other definitions for prospector that I've seen before include "Gold-digger" , "Searcher for minerals" , "Clementine's father, perhaps?" , "One searching for valuable minerals" , "Searcher after valuable ores" .)