I don't know enough about how NASA is already financed. Would selling ad space on the rock cover the cost of the entire mission, less the costs covered from what little funding would come from elsewhere?
Do rocket launches draw enough spectators and cameras to do this? Would the target audiences of NASCAR sponsors be reached? I mean space exploration isn't exactly car racing. Maybe new sponsors would be a better fit?
Say if there were 11 spots and the average cost was $136,363,636? It would work. But the add space might not be worth that much. What would the add space have to cost in order for companies to buy them?
I think this would be far more practical for getting into space in a commercial way:
"From Avatar to Aliens, mining in space has been a staple of science fiction. And now James Cameron, the man behind both those films, is part of plan to make it into science fact."
"The venture, Planetary Resources Inc certainly has some powerful backers: Google founder and chief executive Larry Page is helping to fund the project, as is Google chairman Eric Schmidt. The computer pioneer and former presidential candidate Ross Perot is also behind the company."
