Renting a car is definitely a possibility.

But where will you be staying during your Universal part of the trip? If you are staying on-site, then there will be a daily parking fee added to your hotel bill (and depending on how many days you are there, it can add up.) But if you are staying off-site at a hotel with no parking fees, then given how cheap car rentals can be in Orlando, it is definitely worth looking into that option.

And even if renting a car is a little more expensive, it might be worth it to have the freedom of driving to/from where ever you want, when you want. ^