Assuming a court did find there was a valid offer, if there was an action brought against the store, would vinny's mistake of giving the newspaper the wrong price relieve the store of liability?

I believe the correct answer is the following one - Yes, since the mistake would be obvious to a reasonable person.
Anyone presiding over this case would see that the store had nothing to do with this, and that it isn't really a huge crime as it was obviously just a mistake. So, the store wouldn't be held liable for a small mistake that one of its employees made.