I like your idea of a stock market where you sell your fruit. But I think that it changes too fast. allow the user to try and predict the stock market by making it slower. It would also be visually more interesting to show the changes in prices in a graph. That way you really give the player a “oh now its spiking time to sell” feeling.
Your interpretation of the theme is really smart and I'm curious to see what you will make in the future!