Ok I just had to research this because I wanted to know what on Earth this question was about, and you'll be happy to know the procedure doesn't seem to be surgical.
It simply requires an injection of saline via a drip over 2 hours. The cost of which will depend on the person performing the procedure (I have no idea what the going-rate for this procedure is, but I should imagine it is far cheaper than surgery!)
Bagel Head Surgery
So "bagel head" or "doughnut head' is the term given to this type of outlandish body modification:
You can also opt for "double bagel head":
Like I said, no surgery is required. It's just a saline drip plugged straight into your forehead. The effects wear off overnight as the saline is absorbed by the body.
Who are these bagel heads?
The article I read suggested there was a big "trend" for this kind of stuff in Japan, particularly in fetish clubs etc...
But a little more research reveals that the first person to come up with this idea was actual Canadian.
Personally, I can't see the appeal. But maybe I'm just old and boring!