There are a number of different companies offering generic motorcycle saddlebags. Many of these will fit on the Ninja 250, and range in price from about $75 to about $500. Some are waterproof, some require additional covers to be waterproof.
Here are some pros and cons on the Chase Harper Stealth Bags.
- larger capacity than expected. You can easily carry a liter bottle and a bag of chips in each side. Or a six-pack, minus the cardboard holder (micro-brew for after the ride)
- easy to open from back or front
- made of stiff neoprene material that can hold up a parked bike when it is knocked over by a backing-up. No damage except a scuff on the handlebar ends and a dirt mark on the bag.
- nice, sturdy clips and straps to hitch to the bike
- sleek shape and zoom-y looking position on bike
- pricey - about $110 from the Aerostich RiderWearhouse.
- if you are too exuberant with the zippers, all your stuff might fall out. The bags can open really wide (which is a pro, really).
- you shouldn't carry really heavy stuff in them, according to the manual.
- it is hard to figure out where to hook the straps. This could be a pro, since it gives you some different options depending on your bike set-up
- if you don't hook them onto your bike evenly, they will look a little goofy and lop-sided
- depending on how you hook them on, it can be a challenge to get them off quickly; it's easiest to just leave them on.