The smallest amount that may be rented it's said (5)
I believe the answer is:
least
'the smallest amount' is the definition.
(I've seen this before)
'rented it's said' is the wordplay.
'rented' becomes 'leased' (I've seen this before).
'it's said' indicates a 'sounds like' (homophone) clue.
'leased' sounds like 'LEAST'.
'that may be' acts as a link.
(Other definitions for least that I've seen before include "Smallest in extent" , "Bottom" , "Fewest" , "Smallest in amount or degree" , "Lowest or smallest" .)