Low-priced high explosive put in the detonator (5)
I believe the answer is:
cheap
'low-priced' is the definition.
(similar in meaning)
'high explosive put in the detonator' is the wordplay.
'high explosive' becomes 'he'.
'put in' means one lot of letters goes inside another.
'the detonator' becomes 'cap' (synonyms).
'he' going into 'cap' is 'CHEAP'.
(Other definitions for cheap that I've seen before include "Contemptible" , "A snip" , "Inexpensive or tasteless" , "good value" , "Base" .)