What is the fastest and cheapest way to get from Sanibel Island Florida to the Florida Keys?

Pretty much only by car. Get off Sanibel & take the shortest route east to I-75. Take I-75 South until it intersects with the Turnpike, west of Ft. Lauderdale; take the T'pike all the way to the southern terminus at Florida City. Then take US-1 South to key Largo. You're looking at 4hs+ just to Key Largo plus another half hour to Pennekamp or whereever you go on Largo. Add more time for anyplace else. Add another hour for weekends. Edit -- The Ft. Myers Ferry takes 3.5 hrs to KW & costs $130 per person. Who goes snorkling in Key West?

I could swear there is a ferry that goes to Key West out of Ft. Myers. Check it out - maybe research it on the net but I'm almost positive there is - or at least there was a couple years back.

Ferry out of Ft Myers Beach! Very reasonable! You can also arrange to take it down one day and return on another day -- if you want to stay over in the keys a few days. Get a room down there b4 you go -- sometimes there are no rooms available and they can be expensive so call around. Go to a Keys web site for rooms, etc. there are also coupon books available on Duval Street to save you money! DO take the Conch Train it is a few bucks but welllll worth it !!!! Ask your Sanibel concergier or hotel staff they can help, or try the store keepers in Sanibel, they can help you!

the greyhound bus....

Take 75 south, go to Alligator Alley, go south, have fun.