Octane boost won't hurt it..And no it doesn't cost 10 bucks...At least not when i've done it...I've put mid grade in and used octane booster. It does make a difference. But I wouldn't make a habit out of it...Its just one of those things, you shouldn't really put anything in your tank but premium gasoline...So try to use premium regardless, but to answer your question it won't hurt the car, at least from my experiences with it I haven't had any ill effects from it..I've done it probably 6 times in the last 2 years....