1. I am not sure, but cash wise, around $6.50-7.50 I think. From SFB, around 40-45 mins. Here is some extra advice...got to exit 3, not 6. Exit 3 puts you onto Osceola parkway which will place you near AK area, which is near the All Stars, Pop Century, Coronado Springs and AK Lodge resorts. Its easy to navigate from this point as its less traffic, less lights, etc. Exit 3 dumps you near International Dr. and around Downtown Disney which is a mess at all times, and esp. worse now. Even if your resort is up on that part of property, still take exit 3!
40-45 minutes is optimistic, unless that means 45-50 minutes on the SR-417 toll road plus additional time getting onto SR-417 and driving on WDW property.
I agree that Exit 3 is better for resorts that are along Osceola Parkway (the ones noted above, plus Art of Animation), even though it requires an additional 50-cent cash toll at an unattended exit.
However, Exit 3 is a detour if you are staying at any other WDW resorts. Exit 6 takes you right onto World Center Drive, which becomes Epcot Center Drive when it crosses I-4 onto WDW property. Your GPS is likely to direct you to Exit 6 for any resorts in the Magic Kingdom area, Epcot area, or Downtown Disney area. You will not need to drive on the section of Buena Vista Drive adjacent to Downtown Disney.
3. Not sure about this. If you havent done a rental agreement yet, and you dont have strong ties to National, my advice based on renting at SFB, try Alamo. They are independent from the other rental companies, meaning they have their own separate bldg., they have huge inventory, and at times offer really good deals. We recently got a mini van for the economy price through AAA at Alamo and it was so easy, we were in and out, no time flat.
Alamo has hours that are similar to National. But unlike many airports, at SFB National and Alamo do not have a shared facility with combined operations.
National is walking distance to the terminal (but double-check this to make sure that's still the case).
Alamo is around a mile and half south of the terminal. If you drop your car at Alamo, 3 or 4 hours before it opens, I don't know how you would get to the terminal. Before booking Alamo, I would recommend calling them to see if they have an after-hours return process that does not require you to walk a mile and a half on an airport road during the pre-dawn hours
By the way, it's usually easy to change rental car companies, even if you already have a reservation. You're typically only locked in if you use a nonrefundable rate, typically only found on third-party websites such as Priceline. Just book something new and cancel your original reservation without a penalty.
