Don't expect Mexican shopping to be anything like U.S. They rarely have chains except for high end like Diamonds International. The rest are usually individually owned. In Mazatlan, there is a craft market that I really like. If you go out the back of the market, you can watch the artisans making the things that are available for sale. But, for the equivalent of Dollar Store, check out the outdoor vendors. When you get off the ship, there is a tram that takes you through an industrial area (not safe to walk through). You are dropped off at a round building full of shops, but right outside is a bigger area of tents full of vendors. Rather like a craft show here in U.S. Keep in mind that they expect you to bargain. I had a hard time with that at first, but found that a little humor made it easier. Particularly if you are buying small stuff. Pick up several pieces, as if you can't decide, then ask how much if I buy all 3, or whatever. You can probably find cool souvenirs cheap. Keep in mind that Mexico does not have the kind of mass produced goods that we do.
Do buy a small bottle of vanilla, please. Just to have the experience of knowing the differencwe.
Puerto Vallarta has some small buildings by the ship for local vendors. There is also a huge, and incredibly hot, shopping area downtown. I can't handle that one. Too hot, too closed in and vendors like sharks in a feeding frenzy. Just not worth it to me.
Cabo San Lucas has a large tent area right where you get off the tenders. Their specialty used to be sea glass figures. Used to be cheap, not so much anymore.
Can you tell I've been to these ports? Lived in L.A. for 13 years, and while we did do other itineraries, many times we just did this one since it was cheaper than most others. Watch for pickpockets. I carry ID and most money and valuables in a pouch around my neck. They can watch you spend a dollar, then see where you got the money from and pick that pocket before you can blink. So, some small bills in a pocket or purse, most hidden away.
I love Mexico and have had many happy moments there. People are mostly friendly, warm, and courteous. I was once in the tent area in Mazatlan toward the end of our day and a vendor called out "T-shirts for the grandchildren?" I turned around, hands on hips and asked him in an outraged voice why he thought I looked old enough to have grandchildren. I certainly am, so I then started laughing. As did every other vendor in the place. He tried to give me free t-shirts as an apology. I refused, saying I was just having some fun with him. Stay loose and have your humor handy and you will have a ball there.
Ask me anything else you like, but be aware that I can run off at the mouth, or rather fingertips!