QUOTE(NightHeart @ Jul 18 2018, 11:42 AM)
Don't use invoicing software? You're referring to softwares like Autocount, MYOB, Peachtree or cloud ones like Financio, Biztory & QuickBooks? Then each & every sale will have an physical invoice generated? Only half of my sales have invoices i.e. sale to other businesses (B2B). While my B2C sales don't have any physical invoices. So ideally even my B2C should have an invoice too for my own recording & filing?
Yes I am facing a huge problem tracking my cost, especially to determine my COGS. My COGS fluctuates so regularly to the point that in my inventory, even for the same identical product, they has different COGS because they're bought at different periods. Is there any method to solve this challenge with MS Excel? Barcoding may solve this issue because each item details can be captured & tracked. But woah, the software alone will cost several thousand, the printer will cost several hundred & the stickers will cost few hundreds too. Then not to mention the labor cost to stick the barcode on all the products during inbound phase

Yes, no software at all. That's why filing those invoices back to sequence it's a nightmare. All books invoice starts with different numbering and to keep cost low they just purchase those cash book from stationary shops.
For B2C you could just sum them up once a month and generate an invoice for your own keeping.
Use those colorful stickers that you can find on stationary shops. Not sure what those are called.
Then stick it on every single one of your products:-
Product A purchase on 23/01/2018 cost 60 - Code as A230120180060
Product B purchase on 23/01/2018 cost 70 - Code as B230120180070
When you sell, just key in the code then excel should be able to sort or show the things you need.
Any good stock control need time to implement and a trustworthy staff to manage it without that, the best software also can't help it.
I do have a excel template cater for this due to client requested a control and also me to do stock check
Not sure if it will help you, but if you need the template I can send it to you.