As in the desert, you get one free (4)
I believe the answer is:
arid
'as in the desert you' is the definition.
I can't judge whether this defines the answer.
'get one free' is the wordplay.
'get' means one lot of letters go next to another.
'one' becomes 'a' (**).
'free' becomes 'rid' ('rid' can be a synonym of 'free').
'a' next to 'rid' is 'ARID'.
Can you help me to learn more?
(Other definitions for arid that I've seen before include "Dry and unfertile" , "Dry and infertile" , "Dry raid" , "Desiccated" , "Extremely dry" .)