In my experience, panniers are one of those items where the quality is directly related to price. I have a set of Ortliebs Back Roller Plus panniers that were expensive (~$200) but have been through some horrible conditions -- rain, hail, snow, road salt, long bicycle trips, overstuffed to the point of breaking, grease, oil, scuffed, slid against concrete, kicked countless times -- and they still look practically new and work perfectly. They are completely waterproof, easy to use and well worth the original price.