I wind polywire onto a stick (either 12" piece of timber or a suitable piece of firewood ) using a figure of 8 wind. That way I have a usable wire that can be fed into the plastic stakes. I also make sure that when I take the fence down, I wind the polywire straight back onto the stick again. It can get very tangled if you don't wind it up as you go - ask me how I know that...
It's quite a bit more expensive buying pre-loaded, when it is not too much to create your own skeins.
Sue