Like an expensive car? That's a relief (5)
I believe the answer is:
mercy
'relief' is the definition.
(I know that mercy is a type of relief)
'like an expensive car?' is the wordplay.
I cannot really see how this works, but
'like' could be 'y' (similar in meaning) and 'y' is found within the answer.
'car?' could be 'merc' (short for Mercedes) and 'merc' is found within the answer.
No letters remain.
This explanation may well be incorrect...
'that's a' is the link.
Can you help me to learn more?
(Other definitions for mercy that I've seen before include "Its quality is not strained, Portia said" , "Forbearance" , "Clemency or compassion" , "Shakespeare 'The quality of . . . . . is not strained'" , "Leniency and compassion towards offenders" .)