Hi Benny,
Heres a simple way of pricing your 4-5 selections per race.

Divide the number of career wins into its career starts.
e.g. 4 wins from 21 starts =5.25/1 or $6.25
e.g. 2 wins from 4 starts = 2/1 or $3.00

This only works where all 4-5 of your selections have had one or more career wins, so its probably best to pass up any race that does not qualify under those said conditions

I hope its all right to post this site , it has a priceing program in there that may be of some use to you.
http://www.ozracetools.com/index.php


Cheers.

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Cheers.