Exorbitant lease on urban complex (12)
I believe the answer is:
unreasonable
'exorbitant' is the definition.
(thesaurus)
'lease on urban complex' is the wordplay.
'complex' indicates anagramming the letters.
'lease'+'on'+'urban'='leaseonurban'
'leaseonurban' anagrammed gives 'UNREASONABLE'.
(Other definitions for unreasonable that I've seen before include "Irrational" , "Beyond acceptable limits" , "Not fair" , "Immoderate" , "Unacceptable" .)