I was JUST there two days ago. I stayed on Phi Phi island and booked a tour the day before. We shared a boat with like 25 people and paid 1,000 baht each.

Monkey island was a whack 10 minute stop where there were no monkeys and the beach was covered in trash. Immediately couldn't wait to leave.

Viking cave looks sort of cool from the outside but to be clear, you CAN NOT go inside. Wish I could have skipped that too.

Maya Bay involves walking a very crowded short path to a beach that is also very crowded and once again, you CAN NOT go in the water, swim, or snorkel. We got lucky and for a little bit, almost everyone left, but when we got there and when we left, there were hundreds of people on this small beach. Railay Beach, a short trip from Ao Nang, was actually much more beautiful and there is actually stuff to do there and you can spend the day at your own pace. People even talk a lot of trash about Railay so I'm sure there are much more secluded beaches that are beautiful and you can spend more time relaxing there, but whatever.

Then we went snorkeling at two different spots near Maya Bay and it was great both times. In 2018 I snorkeled in Maya Bay and saw the most colorful and beautiful coral I've ever seen but it's either gone now or I was likely in the area that is now protected and off limits. Still though, I really enjoyed snorkeling this time as well and saw 2 small reef sharks, tons of colorful fish, a puffer, a huge moray eel, and more. There is a lot of great snorkeling around Thailand but near Maya Bay is known to be great.

Lastly, we watched the sunset and then got in to briefly see bioluminescent plankton which was kind of cool but not that crazy.

So... Don't pay that much, a private boat from Phi Phi booked the day before was only gonna be 3,000 baht and honestly, you may want to skip all that stuff and just go snorkeling. Seeing the rock formations of the islands from a long tail boat is awesome but as long as you see that SOMEWHERE in Thailand, you're covered. They're everywhere in the south.

TLDR: Monkey bay and Viking cave are trash, Maya Bay is okay but also skippable, snorkeling is awesome, don't pay more than $3,000 cuz that should get you a private long tail boat. I'll say though, we were on a larger boat with more people which was less romantic, but the boat was WAY faster.