Most modest expense you accommodated (6)
I believe the answer is:
coyest
'most modest' is the definition.
(I've seen this before)
'expense you accommodated' is the wordplay.
'expense' becomes 'cost' (cost is a kind of expense).
'you' becomes 'ye' (historical version of 'you').
'accommodated' is an insertion indicator.
'cost' going around 'ye' is 'COYEST'.
(Other definitions for coyest that I've seen before include "Most reluctant" , "Most modest" .)