My mistake. I did not know much about canning size.
After I last posted on this subject, I went back to the PennMac website and played around with several hypothetical "orders" to see how the shipping charges changed based on what I "ordered" and in what amounts. What I found is that buying just a single item from PennMac, such as a single #10 can of tomatoes, may not be practical from a shipping cost standpoint. For example, I found that I could buy two #10 cans for the same shipping cost as one #10 can. That might be fine if I want two cans but if I really only want one can, there is a premium to be paid in buying just that one can from PennMac. I also added several more items to my hypothetical "order" and found that the more I "bought", the less the shipping charges on a proportional basis. So, I concluded that buying a lot of stuff is better than buying only a few things from a shipping cost standpoint.
The other thing that is important to keep in mind is that PennMac sells a lot of different pizza related ingredients and other items. I think they have one of the best and diverse offerings of pizza ingredients that I have seen in one place on the internet. By contrast, at Escalon, you can only purchase two kinds of tomato products. My advice is to determine what ingredients you want in total, and try to find the best total price, including shipping. If you want a lot of things, it is quite probable that you will do best with a place like PennMac, where you can get everthing in one place, rather than trying to find the best price per item, where you will encounter multiple shipping costs and a higher overall cost as a result.
On the 6 in 1s, it still makes sense to do a total cost comparison between Escalon and PennMac, or any other source. For a few 28 ounce cans of 6 in 1s, it is quite likely that you will do better with overall cost on an equal volume basis with Escalon than with PennMac. But at some point, there will be a crossover that gives the cost advantage to PennMac. That is why you can't really berate PennMac in this instance. It all comes down to what you want to purchase and in what amounts. You might also find that you prefer to have small cans rather than #10 cans. Unless you intend to use a full #10 can, it is more convenient for most people to go with the 28 ounce cans from a place like Escalon. That way, you don't have to find ways to store the unused portion of a #10 can.