Let's say you have a product for sale at $32. Then you have a sale to boost name recognition, and have a coupon for $32 dollars off (limited time offer). Or equivalently, that would be $32 cheaper. So the net price is free ($0). $32 cheaper = 100% cheaper = 1x cheaper. Likewise, 25% cheaper = 25% less expensive, or doing the math $32 - 0.25*$32 = 0.75*$32 = $24.

"cheaper" isn't a defined operation except for "a is cheaper than b".

So the statements "6% cheaper" and "2 times cheaper" are shorts for "it is cheaper, it costs 6% less" and "it is cheaper, you get 2 times more for the same amount of money".

The parent you're replying to seems to have things confused. 100% off isn't 1x cheaper -- it's infinitely cheaper.

No, it isn't sensible, and is certainly confusing, and that is why you should commit to never using that phrasing from this day forward. It isn't like there is a hardship you have to overcome when using precise language. There are plenty of alternative ways to state the desired objective that are clear and unambiguous:

  - The product is now half-priced!
  - The item costs half as much!
  - The unit comes with a 50% discount!