It's tough to say, because you basically have four major areas where boats get bought and sold -- Jacksonville
, Ft Myers, and Tampa Bay. Look at a map and you'll see the problem. These are your major areas, but of course, boats get sold all over the state.
You could locate centrally in Orlando. Not too far from any of these areas, but not very close, either. Or pick one and travel to the others.
The Dade/Broward area, from Miami
up to about Pompano, is probably the busiest area for boat
sales. But then, it is also the most expensive area to stay in, and the boats that get bought and sold there probably average higher prices.
For modest priced boats, more probably get sold on the west coast
between Clearwater and Ft Myers. Though a fair amount are also available in the Keys.
Good to remember that Florida
is a big state, too. If you are based in St Pete, and want to go see something up in the Pensacola
area, that's a good, solid seven hours of driving to get there.
Maybe the best plan is not a fixed base, but move around to different areas, looking at the boats available in each.