I love this idea. I just checked Kijiji and these spools go for $40--100 here. I'll have to call electric companies directly to see if they might be available for free.
We used ours for pigeons and OEGBs when we raised them and they had space to walk around inside the pen. However, we did let them out to scratch around at least once a week. The pigeons would fly out of the door, but were having trouble getting back in since they need to perch and then walk inside. So, we drilled a small hole under the door so when the door folds down, a nail is placed under it to create a landing pad.