As an X-Auditor, I’m not quite sure what you’re looking for - COG is a simple math formula - yes, your individual prices may rise & fall, & that may be of interest to you, but…when your costs are too high, it is generally over-portioning, theft etc…
As an X-Auditor, many folks don’t do a real physical inventory, on a consistent basis, hence poor data…
Looking at some of the data from your POS may tell you some things, but nothing reveals the truth like a real physical inventory…
I use QuickBooks & do a simple inventory every few days - just to keep my eyes focused…if you wait 'till the end of the month to discover you have a problem, you’ll still have that problem next month…