Hill sought by the economy passenger (7)

I believe the answer is:

upgrade

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'hill' is the definition.
(thesaurus)

I can't explain the rest of the clue.

(Other definitions for upgrade that I've seen before include "Get better software" , "Higher-standard version" , "Drug ape to improve" , "Raise to higher class (air travel)" , "Raise to higher rank, or improve equipment" .)

I've seen this clue in the Sydney Morning Herald.

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