Expenses of Greek island trips on vacation (5)
I believe the answer is:
costs
'expenses' is the definition.
(cost is a kind of expense)
'greek island trips on vacation' is the wordplay.
'greek island' becomes 'cos' (I've seen this before).
'on vacation' means to remove the middle letters.
'trips' with its middle taken out is 'ts'.
'cos'+'ts'='COSTS'
'of' is the link.
(Other definitions for costs that I've seen before include "prices" , "Expenditure" , "Charges" , "Overheads" , "Damages" .)