There is a public bus service in Orlando called Lynx and I-Drive has its own internal system. You could try that. There is Lynx Service to the TTC even at very early times in the morning.
A taxi from I-Drive to the Ticket and Transportation Center is $28.00 one way.
My suggestion, however, unless you just can't get out of your reservation, is to try getting a room on Disney property. If price is a concern, the All-Stars have some great rates right now. Check
www.mousesavers.com for the deals.
I did the I-Drive, no car thing once, and it was not very pleasant. The pay transportation service my hotel used did leave early enough for park opening, but just barely. We arrived in the parking lot at official opening time.
They also had a pay shuttle service that picked up from Pleasure Island at at various intervals starting about 8 pm.
The name of the transportation service was "World Transportation Company" or something to that effect.
What I ended up doing was not worrying about getting there before park opening. I just took the earliest bus available from my hotel, paying the one way fare and then stayed on the WDW property all day using internal transportation to get around.
To get back to my hotel, I purchased a one way voucher for the shuttle bus from Pleasure Island, picking a time that was convenient for my plans. 2 nights I picked the last shuttle at 1 am, 1 night I picked the 10pm shuttle.
Also, be prepared that if you want to go to the parks on your day of arrival or day of departure, you most likely will need to take a cab, as that probably involves mid-day travel which is not possible with shuttle service.
A one way taxi from I-Drive to Downtown Disney is $15.00. You can then catch Disney's internal transportation from there. This only works mid-day though, because Downtown Disney buses don't start running till about 9am.
I know this is a lot of info, but I hope it helps.
