I am am unaware of any competition that awards cash. But, an award is not payment for effort or skill, it is a one time only prize. There is no mention of this issue in the FAA Interpretation of section 336.
From the interpretation.
5 Likewise, flights that are in furtherance of abusiness, or incidental to a person’s business, would not be a hobby or recreation flight.
So flight testing is furtherance of a business and incidental to the business. Getting an award for winning a contest, especially if done professionally would make it illegal, as wll as getting money and products from sponsors!