This article is from the Motorsport FAQ, by A H Henry bspahh@midge.bath.ac.uk with numerous contributions by others.
It has probably changed, but according to David Hayhoe's book in 1988
the purse for a race was distributed as follows:
From the starting grid for that race, 0.4 pole ... 0.08 the race
distance: 0.459 results. At the chequered flag, 2.448 ... 0.864
Using the results from the previous two half seasons, 17.5
championship and 17.5 Appearance money is also paid.
This seems to be spread out over the field a lot more than in other
forms of racing.
 
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