Monument not cheap to be rebuilt (8)
I believe the answer is:
cenotaph
'monument' is the definition.
(cenotaph is a kind of monument)
'not cheap to be rebuilt' is the wordplay.
'to be rebuilt' is an anagram indicator.
'not'+'cheap'='notcheap'
'notcheap' anagrammed gives 'CENOTAPH'.
(Other definitions for cenotaph that I've seen before include "Monument to people whose remains are interred elsewhere" , "Monument to those killed in war" , "Empty tomb" , "Monument built to honour soldiers who died in war" , "Monument honouring the fallen" .)