I gotta agree. Most locals know the place to hit for Halloween for scary stuff is Knott's Scary Farm. Their Halloween scene is one of if not THE best in So Cal. They have been doing it for years before anyone else there and usually the couple days around Halloween itself sells out. Something you definitely need to book for. I would quite honestly do that over Universal's event. And it would be a park you can't experience over in FL.
But if you're still wanting to do Universal, try asking the concierge at your hotel. There are shuttles and stuff that run up to Universal. I don't know too much about them as when I lived there I always had my car and drove everywhere. Mother in law stayed at a hotel last year and she was able to get us transport up to Universal through her hotel.