The CDC order states an antigen test is required to reenter the U.S. There are no state-specific requirements.
Any negative antigen test will get you back into the U.S. I'm doing 3 trips with Nautilus, the first of which is the San Ignacio (non-diving) gray whales adventure in February. I've been told by Nautilus staff that antigen testing will be provided free of charge at the airport (SJD). They can't do it at the campground because it's too remote. The test results will be available in about 2 hours. I had to change my flight home to account for this extra wait time. I'm also doing Socorro May 29th and the Guadalupe trip in August. The staff said they will have antigen testing available at the dock (also free) for both of these trips.
I've stayed at the Tesoro a couple of times just as a matter of convenience to the marina and boarding the boat. If you're just wanting a place to lay your head, the standard room is small but comfortable. If you'd like to stretch out a bit, the marina view rooms are much bigger and have a private balcony. The A/C works well and the room is free of bugs. I always book direct with the hotel and don't use third-party sites, such as hotels.com or expedia.com. If you book directly with Tesoro, there's no deposit required and you pay in full when you check in. Cancellation must be done no later than 3 days before arrival. They have several promos going right now, so you'll have to play around with the reservation system to find what's right for you. Since I'm a single traveler, usually AI's are cost prohibitive for me, but my booking for the May trip got me the AI for just $40 more per day. That makes me very happy!
I agree with
@Dan, ask for your room to be near the restaurant and pool. It's a big hotel complex.