The cheapest way would probably be a taxi. Mears Transportation supplies taxi service and they have a fare estimator that estimates $32.45 one way from the Orlando airport to Universal Studios. So for round trip between the airport and RPR, I'd guess about $70.00
Another option, which I use, is a towncar service. There are several towncar services that operate in Orlando. Round trip service will cost around $110 to $120 (some are less) but most offer a free 30 minute grocery stop from the airport to the hotel. We've used Happy Limo, Murray Hill and
FL Tours. My wife and I used FL Tours on our last trip and we were extremely happy with them and will probably use them on our next trip. There are a few more towncar services that we haven't used.
With FL Tours, the driver greeted us as the bottom of the escalator, helped us with our luggage, and guided us to our waiting car. When we used Murray Hill, the driver was also suppose to meet us at the bottom of the escalator, but he was running late and arrived while we were retrieving our luggage. With Happy Limo, you call them after you've arrived and have picked up your luggage. The driver is suppose to arrive in about 5 minutes, but the last time we used them, the driver showed up between 20 and 30 minutes after we called, which disappointed us.
For the return trip, the driver will pick you up at the same location that they dropped you off at the pre-arrainged time.
As for the drivers of the three companies, all have been friendly and informative.