If there are just one or two of you, then the most cost effective is taking Mears shuttle from your resort.
The day you wish to go to Universal, dial "0" from your room phone and ask to be connected to Mears.
When Mears picks up tell them you wish to go to Universal Studios the next day. Give them your resort name, number in your party and the approximate time you wish to go.
You will receive a pickup time and location.
Be there the next day about 10 minutes ahead of time.
Pay the driver $16 CASH per person.
You will be transported to Universal.
Upon arrival you will be given a return ticket. You can make arrangements for a return pickup time at that time or call the number on the return ticket 2 hours before you wish to be picked up.
At the return time, go back to the place where you were dropped off and you will be returned to your resort.
This is a shared ride, so you may go to different resorts both directions.
If you would like to purchase your Mears tickets with a credit card, you can stop by any Mears desk at the airport before boarding Magical Express to purchase transfers to Universal, but you still need to call the night before to make the actual reservations.
Another option is a 24-hour car rental from
Alamo or National on Disney property, but just have to weigh the costs. Don't forget to include gas and the $12 parking fee at Universal in your calculations.