Where are you getting the information that this price was terrifically cheap? Henry himself said that he bought muslin for only 5 shillings. This if 4 shillings a yard more. Perhaps this basically a standard price for fairly good quality material.

She comes over to where they're talking and interrupts them in order for Catherine to take a pin out of her sleeve and comments outright about how much she paid for it. He replies that he would have done the same and then she takes over the conversation and doesn't let it wander away from her again. Just not seeing Henry's rudeness here.