'P' announced after a race (8,5)

I believe the answer is:

starting price

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'p' is the definition.
Both the definition and answer are singular nouns.
Maybe there's an association between them I don't understand?

I don't understand the remainder of the clue.

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(Other definitions for starting price that I've seen before include "Final odds as race begins" , "Racing tipster (anag.)" , "Key information for better" , "Odds on horse at beginning of race" .)

I've seen this clue in The Irish Independent.

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