Any public land that may hold Osceolas is going to get hammered. If you are just in it for the experience and a chance, I would say go for it. But, if you don't want to come home empty handed, if you think of what it is going to cost to keep trying to kill an Osceola on multiple trips on your own, it's probably better to bite the bullet and pay an outfitter.
Either way, if you want the contact info. for a great guide, I can send that to you, I also can give you a start on public land, send me a PM, I don't like putting this out for everyone else to see.