My impression of the intended rules is that comments need to have "substance" as to constructively carry a conversation. Pointing relevant things out like the price, and making a comment in the form of a joke is perfectly normal in a conversation. You might not have a response but other's may, and indeed you can see a few people continuing the joke for fun.

It's the comments that have no substance, the "no you're wrong" kind that doesn't actually _say_ anything, or specifically baiting for heated responses in flame wars that are issues.

You might not like the jokes, but this type are definitely allowed.