I didn't have the $3,000 for an excursion to camp the largest cave in the world, so I settled for #4 at less than 1/10th the cost. A bargain by any means and an amazing experience. Jungle trekking, cave hiking, rappelling, and amazing Vietnamese food at every turn. Couldn't have asked for a better two days.
EDIT: Sorry if the original OP was too brief. I made the thread the night I got back and was so exhausted I barely had the energy to get that much out. But here's some more info:
The tour sets off out of Phong Nha Ke Bang. They pick folks up from where they're staying and there's a briefing at the tour hq. It's about an hour's bus ride to the trailhead.
The hike is one big loop with the cave in the middle. It's about 12km out, then 7km back. The hike out is a bit strenuous but not so bad. Be prepared for a shitload of leeches, though. They're tiny, and they don't hurt, but they're annoying as hell. Long sleeves, long pants, high boots, high socks all help. But it'll still happen. Just make your peace with it.
Hiking inside the cave itself isn't strenuous at all, though it can be a bit slippy at parts, so expect wet feet. There's some abseiling / rappelling, but nothing dangerous and honestly quite fun. The campsite is set up before you get there. The company has a group of guides / porters that go ahead and pitch the tents, cook the meals, all of it. Speaking of which, the meals are delicious. A good variety of Vietnamese food, from pho to nem lui (rice paper wraps) to banana crepes and various veggies. Really solid meals all around.
You spend one night in the cave and set off for the return at around 9:30 in the morning. The hike back is pretty brutal. You're basically covering the same elevation change, in almost half the distance. I'm an avid hiker in pretty decent shape and I got my ass handed to me by the return hike. It's basically a straight uphill climb for a good stretch. And since you're in a group, you're kinda beholden to the group breaks, unless you wanna be That Guy and hold things up for the poor guide stuck covering the rear. (I was That Guy for a bit of it). The climb eventually levels out and has a mix of ups and downs that aren't too strenuous, before a final huge push. It's pretty exhausting. Worth it, but exhausting.
After you get back to the tour company HQ, they give you this cool little passport and a pewter medal which is actually kinda awesome. And that's mostly it.
I won't mention the tour company, but as I'm pretty sure it's the only company authorized to tour the Hang Pygmy cave, it shouldn't be hard to google.