Wouldnt you also need to know what store location, how distant the store is from the shopper, ho many they have done before, what the weather is (a shop performed in a nor'easter or a snowstorm or a fire is worth more than a fine weather shop), and a lot of other factors. If by some wild chance, you found out the bonus from someone who does audits at the same store gets, what would you stop you from bidding $5 less in order to get the job? Frankly, I can't see how you are going to get any useful information from your question.
You need to decide how much of a bonus is required to entice YOU to do one. That is really all that matters.
Shopping Southeast Pennsylvania, Delaware above the canal, and South Jersey since 2008