Always seems to be the "older" ladies that do this (and I'm fast becoming one of those gals as I type). I think they do that to try to embarrass you into lowering your prices enough so they think they are getting a bargain - prices in their day were considerably less. I remember agonizing over material at Franks Five and Dime that was 75 cents a yard vs. 50 cents.
I generally don't say something but if they keep yappin' and they get kind of loud, they deserve whatever rude comment you throw their way in return.