Thinking about a Johnson trade, I think the Bedard to Seattle deal is a reasonable place to look. Both were coming off of very good career years. Bedard was a few years older. The Orioles got Adam Jones, George Sherrill, Chris Tillman and two other prospects. That's a pretty enormous value. I don't know who it would take, if Florida is even going to consider a trade, but I think that's a good comparison.
Of course, Bedard was a LHP and had played more full seasons.