Hey Scott;
I have a bunch of Grand Slams (both Single, and Double) under my belt, and am nearing the completion of my third US Slam (49 states, excluding Alaska), but I've never been to Mexico or Central America for Gould's and Ocellated turkeys. Nearly all my birds are taken on public land. With as many high-quality places to turkey hunt as there are across this country, it's really not that difficult or expensive to earn your Grand Slam...especially so if you choose to camp out, and cook your own meals. Licenses (while too-damned high) are fairly affordable, so the biggest obstacles are time off from work, and time allowed away by the family. I travel in a Sprinter van, so my lodging is right where I park each night, and it gets good mileage, too. The most important part of any such endeavor is pre-trip planning and scouting. There is a wealth of information out there online that can save you lots of legwork, so don't be afraid to ask questions of the local wild turkey biologists in the places you intend to hunt. Also, feel free to ask me (by pm, please) questions about particular places. I am always happy to help out a fellow traveling hunter. I can also supply you with a guaranteed pay-hunt for Osceolas (no shot, no pay; simple as that).
Good luck!
Doc