I think RFID tags are too expensive to put on every product. I may be wrong on this.
https://www.alibaba.com/product-detail/China-Professional-ma...
I don't think that's actually what Amazon Go is doing though.
I am sure that amazon/walmart/tesco/whoever will need more than 1000 at a time and so obviously get a larger discount. Probably down to well under a penny or two - starts to make a lot of sense when you factor in the other benefits (lower staff, easier stock-tracking/taking etc)
So, it would require a $10 item to break even on a €0.10 tag.
Basically if Savings from reducing sales persons > Cost of New Technology, you'll add the new tech.