“Cheaper” means “less expensive”. 2x cheaper means 2x less expensive, or less expensive by a factor of 2, or 0.5x as expensive. I can say 2x shorter, 2x slower etc. and I don’t see a problem. Everyone I know would understand that it’s the reciprocal of the original price, although I get that in a country whose president can say he slashed proces by 500 % without instantly having to resign, fractions and percentages might have to be specified but that’s longer to say for the same number of significant figures.

Yes, I can find people debating “two times cheaper” (English) but not “zweimal billiger” (German) or “dvakrát levnější” (Czech), in fact the phrase is often used in promotional material. The only results suggesting it’s wrong are English Reddit discussions’ automatic translations to German or Czech, and Google’s AI summary that cotes them.

I won’t stop using it just because people with inferior education sometimes don’t get it. Similarly, I provided the metric value and conversion rate, it’s Americans who need to practice mental math.