Expensive contract secures church for race (12)
I believe the answer is:
steeplechase
'race' is the definition.
(I know that steeplechase is a type of horse race)
'expensive contract secures church' is the wordplay.
'expensive' becomes 'steep' (I've seen this before).
'contract' becomes 'lease' (lease is a kind of contract).
'secures' is an insertion indicator.
'church' becomes 'ch' (common abbreviation).
'lease' going around 'ch' is 'lechase'.
'steep'+'lechase'='STEEPLECHASE'
'for' acts as a link.
(Other definitions for steeplechase that I've seen before include "Running event over hurdles and water jumps" , "Race with obstacles to be jumped" , "Type of horse race" , "Non-flat horse race" , "run?" .)