My sister almost got them but then when she was told that its really expensive to get nice ones it changed everything. I think it was $500 or somthing like that. I dont know for sure. But me personally have never got them..... maybe because im a boy.
There are apparantly many different kinds. She got human hair (really good extentions) that cost her $1600.
I'm sure there are much cheaper methods--but from seeing people wearing them, you can definitely TELL when someone has bad hair extentions in. Plastic hair looks like plastic hair, y'know?
I wear a mullet wig for fun from time to time....seeing as I have a shaved head, I'd consider them extensions, cost me $10. And they normally stay on til I sober up.