The Simplest and Cheapest Barbed Wire
I've seen quite a few different ways of making barbed wire, all claiming to be easy and cheap but most of them involve multiple wires being twined together and if you mess up, all you have is a nest of tangled wire. Even when you do suceed, it usually is inconsistent and looks rather bad.
So I had an idea the other day, why not use wire that's already twisted?
All you need are two things: "pipe cleaners" (they come in bags of like 50 at a craft store, pretty inexpensive)
...and a lighter (or a razor, but it is harder)
Twist the pipe wire around a highlighter (it's what I did, but it was only large enough to top blockades, if you want it to be a blockade itself, use something bigger)
Remove from the highlighter and take it outside (nasty black smoke comes off the stuff, if you don't like it, use a disposable razor on the fuzzy/soft pipe cleaners for the effect) and burn all of the fuzz off.
*seriousley, don't breath in any of the smoke, I did on the first run and my nostrils felt tingly/burning and I could smell something awful for hours.
You now have barbed wire!
If you want it to look better, drybrush it with a metalic silver over a black.
And that's all there is to it!