A buddy of mine was renting cars from his collection when Michigan had the movie incentives. His wife's primered 1966 Pontiac Bonneville Convertible was featured in a Kid Rock music video, if I remember correctly. He told me he would get $250/day for a vehicle. He would go there in person, every day, to make sure the vehicles did not get damaged.
In my opinion, the only way to make any real money is to rent several vehicles for the same event. This guy has about 30 vehicles, many which are military, fire equipment or police vehicles. So I think he would rent more than 1 for an event to make it worth his time.