Hi Christina,
I am just back from 2 weeks in the Keys on Sunday, I caught a few bones wading the flats on early morning tides, the problem with going in july is the water tempratures have gone very high up on the flats (up to 32-33C) and the bones are found in deeper water and only move up onto the flats really in the early morning, if you contact bud' n Mary's in Islamorada, and try speak to Richard stancyzyk (
http://www.budnmarys.com)
and explain what you want to do he will give you the best advice and guides, you could also contact rich tudor he captains out of the marina at world wide sportsman at mile marker 81.5 in Islamorada, or matt bellinger out of the holiday isle marina around mile marker 84.
don't be surprised to only get only 1-2 shots a day at a fish (but they could be up to 15lb in Islamorada), and I would suggest you find a field somewhere, put the top of a plastic bucket on the ground, and make sure you can land the fly on that every time, from any angle, from any distance up to 30yd, in winds up to 10-15 kts, if you can't you would be better off using conventional tackle.
you can do 4-6-8 hr trips and they will cost you 450-500 dollars a day + tip.
http://outdoorsbest.zeroforum.com/zeromain?id=1
that is a link to a great forum, scroll down to the florida keys fishing reports and general info, and you can put up requests, search the data base, meet people to share charters, or even make contact with locals who might take you out.
have a great trip, and I hope you avoid the hurricanes.
Dave