> Buying UPC codes from eBay or other websites. This is the easiest way and it costs only 2$ for a UPC code! I did little bit research and found out that many people are buying from eBay-like sites. So i decided to go with the second option.
DO NOT DO THIS. You will get banned from Amazon and the codes you bought will be worthless -- not just the money but the codes printed on the products that will have to be redone.
Registering with GS1 is the way to go if you're serious; the cost is usually much less than $250, depending on where you are and the size of your business; and then with the registration you can generate as many codes as you want.
Or you can register a brand with FBA, and then apply to have no codes; if you only sell on Amazon it's a good option. Your products will only need an FNSKU number than Amazon generates for you.
See for example (many articles on the subject exist, just Google it)
https://amzadvisers.com/amazon-gs1-barcode-requirements-are-...