I know that both times I have stayed in a Disney resort & traveled to Universal, I've used Mears. They pick you up at your hotel, & bring you to the transportation area at Universal. You can set a time for return when you book your trip, or you can call them a couple of hours before you want to leave & they'll give you a time & a gate number. I think it was $12 per person round trip. It took alittle while to get there because the bus also stopped along International Drive hotels, and at Sea World, but if you get an early bus, you get there in pleanty of time for opening (we went on a Halloween Horror Night last year, got to the movie park at opening, had dinner at Emeril's and spent the night at Islands of Adventure. Mears picked us up at 11 that night, I believe)
Good luck!
Robyn