For a start, half of us are in debt! (5)
I believe the answer is:
debut
'for a start' is the definition.
(debut is a kind of start)
'half of us are in debt' is the wordplay.
'half of' suggests halving the letters.
'are in' means one lot of letters goes inside another.
'us' cut in half is 'u'.
'u' inserted within 'debt' is 'DEBUT'.
(Other definitions for debut that I've seen before include "Appear in public for the first time" , "entrance" , "where one began" , "First appearance in society" , "Start -- launch" .)