I'm sorry I don't know the name of the company that puts on the 'tour', but as I said, the boat's name is Luna de Miel (I think they have another as well). It leaves and returns from right 'beside' the ship - If your ship is tied up facing shore you will see the tour dock just off the port bow (you could practically throw a stone over). I'm sure you can't miss it if you ask around, esp. with the name of the boat. From what I gathered, it was a 'middle of the road' boat. The passengers we about equally split between international tourists and 'well off' Mexicans in PV for hollidays (we were the only people off the Ocean Princess because nobody else knew about it).
We did have to pay extra for the horses; I believe it was about $10, but quite worthwile. You can walk up to the waterfall & pool but I wouldn't recommend it. It's quite a haul, it was HOT and parts of the trail are steep and dusty.
I drank AT LEAST $25 worth of beer and rum & coke ($100 at ship prices...lol)... nobody got drunk though... just a lot of happy people, and the crew were into the party! (all except the captain). If you want to snorkel, take your own gear - the stuff they have is junk; and I didn't want to use one of their snorkels no matter how well it's cleaned and disinfected. Los Arcos is really kind of a 'magical' place to dive.
If you go... take a wide brim hat and something to use as a cover-up (long-sleeve shirt), sun block and shorts or pants to change into for the 'cruise' back - you don't want to spend all day in your bathing suit.
It was the most fun of the 22 days we were on the cruise (and reasonably priced)! Enjoy!