I've done something similar, but I had the OK to say I was doing a research project if approached by an employee.
My method was this: I took pictures of everything I needed with of course, verifying you can read the product information (weight, brand, etc.) and price tag.
From there,
1. I extracted all the pictures to my laptop at home,
2. Used the names of the pictures into a spreadsheet,
3. Added columns that identified everything shown in the picture. Ex. Brand, product, weight, price.
After spending the time to get all that itemized, I could apply formulas to figure out which was most expensive, most expensive by unit price, etc.
I don't see any issues being noticed that you're taking picture, especially if you're in a large grocery store and / or in during a busy time.
Very infrequently shopping the Greater Denver Area, Colorado Springs and in-between in Colorado these days.