I would say their chances of renting a boat to try living aboard in different places ranges from "darn slim to nigh impossible" as the saying goes. The way most folks would choose a liveaboard location is to SAIL IN on their own boat. Moor or dock for a week, check out the area, sail on to the next spot, and at some point either sign a lease or go back to the place they liked best.
The west coast of Florida will cost them way less than the east coast (at least, less than anyplace south of Jacksonville) but the trend all over the US and especially in Florida in the past 20 years has been "I own the water, get out." Some of the local cruising guides and clubs may be of better use to them. Coming from Maine to Florida...land to sea...Big change. They might want to come down and visit you for a week or two, and in that time, spend all day every day driving to different towns, walking the docks, checking the charts, and asking around ot get first hand information. Way cheaper and faster than coming down on a boat and sailing from one to the next. And, I'd suggest, they should come down NOW in the low season to see the worst of the weather, too.