How much does one hair extension cost?

A couple of weeks ago I got a purple real hair, hair extension at a career fair. They put a little ring around the top of it and then used pliers to squeeze the ring and clip it in. It was supposed to stay in for about 3 months but sadly it fell out. I have blonde hair an the purple looked really pretty in it, I really want another purple streak like that but I don't want to dye my hair because I would like to donate it to cancer later in life, I want to get one purple real hair extension, the kind that they fuse Into your hair, about how much do you think ONE would cost????