Gesso - yes or no? What is a possible budget alternative?

Hi all, I hope your week is going well so far :)

I wanted an opinion on alternatives to Gesso - I don't do many pbns, so I feel like purchasing it will be a waste. Is there something else I could use to prep my canvas, like just an acrylic white wash perhaps? How long does Gesso store for once opened?

I started a pbn 5 years ago but never finished (my son was born, life ¯\_(ツ)_/¯), and the issue with streaky paint, numbers coming through etc was a pain. I did find adding acrylic fluid helped a lot. When I eventually go back to finish that pbn I am going to try using my white Posca marker to reduce the numbers showing through, but I'm not sure if I need to go the Gesso route for the new canvas - For reference, I've ordered a small custom pbn from Amazon, so I doubt the canvas will be top quality, it's just for a bit of fun as its a portrait of my Bichon, Pippin :)

Bonus question: What other materials/mediums is Gesso good to prep in your experiences? I would mainly paint with watercolours (not good there, obviously), but I also do rock painting with acrylics, and I use oil pastels on paper, as well as alcohol markers. I don't mind buying it if I can use it in other projects or if it will keep.