Take the bus. It's the cheapest way to make this trip, and the price gap is usually bigger than people expect.
Tickets start at around $30 (€24) compared to roughly $154 (€124) in fuel and tolls — a saving of about $124 (€100). The journey takes 6h 35m versus 5h 39m by car, so you'll arrive a bit later, but you can use the time productively rather than spending it behind the wheel. No parking to sort, no fuel stops, and most coaches have Wi-Fi and power outlets.
Direct services are operated by Itabus, Autoservizi Salemi, Salemi, BlaBlaCar, Autoservizi Salemi Srl.
Driving is worth considering if you're on a tight schedule, travelling as a group (where fuel costs split several ways), or want the flexibility to stop along the way.