Hi reddawg, and welcome to the DISboards.
Would these be consecutive days that you will be going to USF/IOA? If so, I would recommend staying onsite at Universal rather than commuting back and forth each day. No need to rent a vehicle, no parking fees and you would get front of the line access.
But, if you don't want to stay at Universal, then the next best thing would be to rent a car for the 3 days and drive yourself back and forth.
If the days are not consecutive, then a taxi would be a good alternative. It's not the cheapest but it would be more direct.
The cheapest way would be to go by Lynx bus. However, you would be married to the bus schedule and you would need to make transfers. The commute could take quite a long time.