I have down the grand slam twice, once with a bow and once during a single season with a gun. I like hunting turkeys, so the slam is simply a nice reason to go different places. My next goal is the super slam, taking a turkey in every state they exist. Did I mention i like to turkey hunt?
I haven't registered any of my birds, as it seems pointless unless you want to get the pin, but that is up to you. I got turned off when I realized some people had registered more than 50 slams. The eastern is hands down the hardest to get followed by Osceola, but that is predominately because of land issues and cost in Florida. If you are looking for a good relatively inexpensive Osceola hunt try Triple M Outfitters in Palm Bay. He has lots of turkeys and property and is a genuine person. There are PLENTY of cheap options or DIY options for Rio's and Merriams. I have done it both ways, usually simply paying a semi-guided fee for food and lodging which was as cheap as getting a hotel and feeding myself, plus I got access to private land. To each their own. As I travel to more states it will be mostly DIY or with friends or trade hunts.
I am heading to Mexico this spring for Gould's. Much like Merriams and Rios they typically aren't what eastern hunters consider a typical turkey hunt. They are usually in flocks and it is more of an ambush. I have certainly called in tom's from a distance like an eastern of both species, but mostly you get in the area they want to be and wait for them to show up. Each hunt is still pretty fun. The Royal slam counts wherever you take a Gould's, Arizona or Mexico. Arizona is tough if you haven't been in the draw for a while and by the time you pay for a license in Arizona and the points for ten years it would be cheaper to go to Mexico as you can get hunts for ~$1500.00 if you dig. The coolest bird to hunt and a hunt I am doing in spring 2016 is the Occelated. Not a turkey hunters hunt for sure, but I am looking forward to hunting brockett deer, guan, and curassow when I am there and I found a great relatively inexpensive place to do it at.
Good luck with whatever you choose to do. If you ever need any pointers, feel free to PM me. I don't post much but I do lurk around.