Howard Leight 'Max' (SNR 37) or 'Laserlite' (SNR 35) off the shelf ear plugs have come out on top in various independent reviews, (as long as they are worn correctly) beating both ear defenders & moulded products...a quick search on the Internet will give you various H&SE reports. In a nut shell, not all products are made equal, not all manufacturers tell the truth with regards to their SNR rating & price is no indication of the level of protection offered...I was surprised to learn that the moulded products tested generally didn't fare that well against much cheaper products. (Stopped using mine on the strength of it)
If I find the test reports again, I'll post a link.