You can construct a set of bicycle panniers in under an hour using two kitty litter buckets, hardware-store hooks and reflective tape, along with a cordless drill and nuts and bolts. This will yield cheap efficient storage that can also ugly your bike to discourage theft.
Bicycle touring site Crazy Guy on a Bike shares the kitty litter pannier method that the author has used on his extensive rides throughout North America. The panniers cost less than $US10 to construct and last through 6000km (three years for the author) of hard use before needing to be replaced.
The link below takes you through step-by-step instructions, but essentially all you're doing is measuring and drilling holes to mount the hooks, attaching the hooks with bolts, and adding reflective tape on the back. Keep in mind that to attach any type of pannier or bag to your bike you will need to have a bicycle rear rack — you can get one for around $US30 at bike shops or from Amazon.
Bike Buckets - An inexpensive pannier system you can make [Crazy Guy on a Bike]