Someone put a bunch of wire on the Exchange shelf. It looks like about the right gauge and it is definitely solid. You will have to peel a lot of insulation to liberate it though.
By the foot is the easiest way to go, the plastic shielding is really easy to peel off and its what I do when I am playing with copper. Also, you can sometimes get lucky and find one on their mis-cut shelf. Sometimes someone cuts a length of wire but then decides against the purchase, so they put in on a rack outside of the wire cutting station and discount it. I always check the discount rack first.