To appear semi-nude for fifty quid is useless (4)

Ross

I believe the answer is:

null

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'is useless' is the definition.
(thesaurus)

I can't explain the remainder of the clue.

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(Other definitions for null that I've seen before include "Not valid" , "Invalid; empty" , "Having the value zero -- void" , "Useless - nothing" , "Without value or consequence" .)

I've seen this clue in the Evening Standard.

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