Sorry to hear about your health. Craigslist can be good or bad but has a lot of lowballers. That's a pretty in demand lens so I would think if you can deal with the shipping you would probably get a decent amount on Ebay. I've bought and sold a lot of stuff on Ebay and rarely have problems and there's always risk of numbnuts or scammers. Or maybe try B&H's used section.
I also have a D800 but have been switching over to Sony. A7R is great. So much nicer to have smaller and lighter everything. Smaller camera and lenses need smaller and lighter tripod and bag. My DSLR backpack was over 30 lbs. Now I just carry a small sling and super-small Mefoto tripod. Probably under 10 lbs for everything. What a difference.
Hope whatever you do works out for you.