Which of these is an example of a substantial effect on interstate commerce?

The correct choice illustrates a clear connection to interstate commerce due to the production of goods intended for out-of-state markets. In the context of the Commerce Clause, activities that have a notable effect on interstate commerce can be regulated by Congress. A factory that produces goods for sale beyond the state's borders signifies engagement in interstate commerce, emphasizing the interconnectedness of local production and national markets. This is a key factor in situations involving economic activity and federal oversight.

The other options lack this substantial connection to interstate commerce. A local community event, while possibly beneficial to the local economy, typically does not engage in or affect commerce that crosses state lines. The price change of local agriculture may influence local markets but does not automatically extend to interstate commerce unless it significantly impacts a broader market, which is not indicated here. An individual’s personal hobby generally does not involve commerce at all, especially not on an interstate level, and therefore does not present any substantial effect on interstate commerce.