Like I said, I don't think I've ever seen them. For instance, you can't go into a Walmart or Best Buy and ask for a cash discount. Maybe a small business offers them, but I live in a small town (pop < 4k) and our grocery store and hardware store don't offer a cash discount. Neither do our gas stations offer a discount for paying for gas with cash, as the other reply mentions.
I'm not disputing they exist, just that it's exceedingly rare and not the norm.
> My barber has a sign with a cash price, a Zelle/Venmo price, and a credit card price.
I'm half joking and half serious, is he intentionally trying to confuse customers? Why do Zelle/Venmo have their own prices, and what price do I pay if I just want to pay with the debit card on my phone?