In reply to Roadrunner5:
It's a mixed race. The first three finishers regardless of age or gender should take the first three prizes. That's the most equal way of doing it.
Then there should be prizes for other categories if the organisers see fit.
What are we rewarding? People who've had a go or people who have won.
It would be unfair if a Woman came second but was only given the Woman's first prize and the next Man was given a higher prize than her for being second Man.
Or is it two races run separately. In which case assuming the prize money is given by sponsors, then they should get equal prizes, and men should be aware that there is no point out sprinting a woman for the line (although I know a few women who'd be unhappy if a man eased off and 'let her beat him')
If the prize money is calculated from the size of the field, then do the calculation and make sure that the women and men get the same proportion based on male and female entries. You could take it a step further and calculate all the age group prizes the same way.
Lots to think about. Ultimately it's not an equal race.