even with paying for parking at universal, it would be cheaper to drive from disney to there. i am assuming there are at least 2 in your group?
you need to avoid the traffic on I - 4.
don't travel in rush hour.
leave disney at 7:15 and miss the rush.
you could be at the universal garage line within 20 minutes (if no traffic.)
be in the line for the parking garage by 7:45 and you should be the 4th or 5th car in line. the garage opens promptly at 8:00.
you will be parked and at the turnstile by 8:20 then.
if you start at IOA, you might get in around 8:30ish. official opening is 9:00.
there are more rides open at IOA at 8:30ish than the studios side.
if you take a cab, it depends how many in the cab and the length of time in the cab, besides the mileage cost. after this post, i'll give you the link to estimate the cost of the cab.
you would be dropped off in front, where the cab sections are at universal.
you would get the cab at the same place when returning to disney.
it's really a personal choice. if you don't want to drive because you are not familiar with the roads, i understand that. you can get excellent directions here from metro, phamton and other homies that live locally.
both of them do disney and universal and know the driving roads quite well.
