The side bag hauler kit is the most affordable way to go. Use your own bag of any style and nearly any size. Even if you use HARD PANNIERS I'd suggest carrying the Side Bag Hauler Kit. I've seen a guy once hit a boulder and rip his pannier off. He ended up strapping it back on with paracord. It barely stated in place and he had to keep adjusting the knots. A side bag hauler kit would hold a busted pannier on place firmly and confidently without fussing with knots. I always carry a kit with me in case I'm running around town and end up buying something I shouldn't have while riding. I can usally get it home though.