>- What if people don't want to pay for the extra bandwidth?

Bandwidth costs nothing. Unless you're doing something really weird the HN traffic shouldn't cost you a cent.

>- What if your site contains lots of bandwidth consuming content? (read: large/many images)

Bandwidth still costs nothing, come back when you're streaming lots of 1080p video.

I know from experience that it does, yes. HN is a burst of traffic but it dies down quick, within an hour or two. You're not going to exceed your limit or break the bank unless you're being ripped off.