You get one free, like in the desert (4)
I believe the answer is:
arid
'desert' is the definition.
(thesaurus)
'you get one free' is the wordplay.
'you' becomes 'a' (I can't explain this - if you can you should give a lot more credence to this answer).
'get' is a charade indicator (letters next to each other).
'one free' becomes 'rid' (I've seen this before).
'a'+'rid'='ARID'
'like in the' acts as a link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for arid that I've seen before include "Rainless (region)" , "(Of climate) dry" , "(Of land) very dry" , "Dry and withered" , "Tedious; short of rain" .)