Its definitely cheapest to organise the whole trip yourself. Can be done easily over internet if you're organised :)
Write down
Everything you need to pay for ( hotel, flights, insurance, ESTA, parking in UK etc)
everything you want to do.(Disney, NASA, water parks, keys etc)
Then look at travelling around Florida to see if you need the hire car. Sometimes its cheaper to hire than to have transfers, and definitely more convenient to get to places outside of the immediate area.
Then itemise it all on a spreadsheet (i luffs me a spreadsheet). Shop around. Keep notes about company name, website, price etc
Then start booking!
Get email confirmations for everything. Make a folder in your email to put it all.
Scan every document (passports etc) email them to yourself. Put it in the folder!
I then go OTT and create an intinerary one for us on holiday, one for family at home
Ours includes all booking refs, flight nos, times, hotel addresses etc in date order. And a rough plan of the days (this is fairly fluid, but helps me to have an idea of what is supposed to be happening and when)
I print ours out, have it in a folder with all other documents (in the order needed
) and that stays with me. noone else can be trusted and they'll mess the system up
Second basic itinerary is for family at home, so they have dates, flight info and hotel contact info. So they know how to get hold of us "just in case". Plus my FIL loves to track our flights, so he always gets the flight number!
Too organised?? 