What month are you going & how long are you in port ?
A great way to get to Erice is by taking the cable-car (funivia) which climbs from the outskirts of Trapinani to the town wall of Erice. It's a lovely panoramic 10 minute ride, The funivia runs every day from morning to night, except Mondays when it usually opens only at 2pm.
The cable car station is about 3 miles from central Trapinani so you'll have to get a bus or taxi.
What places are you wanting to visit ?