Former writer occasionally seeks costs (8)
I believe the answer is:
expenses
'costs' is the definition.
(I know this)
'former writer occasionally seeks' is the wordplay.
'former' becomes 'ex' (prefix meaning former or onetime).
'writer' becomes 'pen' (something which writes).
'occasionally' means one should take alternating letters (letters taken at regular intervals or occasions).
The alternate letters of 'seeks' are 'ses'.
'ex'+'pen'+'ses'='EXPENSES'
(Other definitions for expenses that I've seen before include "Costs incurred in the performance of one?s job" , "Costs incurred on behalf of, say, employer" , "Outlays" , "Reimbursed money spent in the course of work" , "Reimbursed monies spent in the course of work" .)