The Mexican Rivera board is here:
https://boards.cruisecritic.com/forum/124-mexican-riviera/
If you make the "main board" your home as you enter Cruise Critic, you will see the tremendous amount of info available to you:
https://boards.cruisecritic.com/
If you look at the Mexican Riviera board, where these topics are regularly discussed, you will see many posts NOT recommending snorkeling in the Mexican Riviera, as the visibility isn't all that good.
Rethink your searching. First, find out who has an office in Civi. (None are actually in the port, but there are some in the town.). Then rent from one of those operations at Rome Airport. Try Hertz, and Autoeurope.com.
Be very specific on hours when you will drop off...the office hours in Civi seem to be limited, particularly on weekends.
Don't plan on driving within Rome. Its very complicated.
I doubt you will find much in the $150 range downtown...you will need to, as discussed here frequently, probably stay near the airport.
Some threads about Seattle hotels. First one is about 6 threads down the board:
About 6 threads further down, still on the first page. Note the name of this thread:
If you look around the board there are MANY threads on Seattle hotels. But, I think you will be disappointed, as your budget doesn't match very well with the standard prices downtown. Seattle is not cheap downtown.
It is going to vary, potentially by significant sums, depending on the cruise line and the relationship the various cruise lines has with a given travel agency, plus what portions of their commission travel agency is willing to share with the customer.
There is no way around just flat out doing the research.
I would be researching to see if the brand is still available, and then go forward with planning how to acquire it. If you are talking about chocolate covered macadamia nuts, they are sold everywhere.
You can take your food from the Lido to the aft pool. The mid ship pool roof may be open, weather permitting, for eating from the several eateries around the pool, and the Lido, on the 9th or 10th decks. Upper, outer decks for lounge chair eating.
Just a little Google mapping would answer your questions. The Costco and Walmart on Maui are near the Kahalui port, not the Lahaina port...45 or so minutes away.
The Costco in Honolulu is about a 1.5 miles from the Aloha Tower. Walmart is a little over 2 miles.
Kona's Costco is over 4 miles away, outside of town. Walmart is about a mile away.
Walmarts and Costcos have websites that give you locations and directions. Google Maps backs those up and helps you visualize where these things are.