I know that you can buy them for almost nothing, but if you fancy being a bit creative, using up those odd socks and getting a hair donut for virtually nothing then carry on reading!!
I suppose if you wanted to make it tighter then you could roll another/part sock round it, but it is your choice. Mine cost nothing to make and as my hair is around shoulder length (I'm getting it cut on saturday) just makes doing my hair a bit easier!!