I think it is southern uk slang if my etymology serves me right.
EDIT: also, we usually use punter (nowadays anyway) to refer to someone buying any service. Usually it is used in the context of smaller businesses (market stalls, sideshows, fairs etc.)
In Australian Rules Football, and to a lesser extent in Rubgy and Gaelic football, a "punt" is a kick which is most commonly used in an attacking manner.
As a verb, "Punt" can also mean:
+ A kick of a football
+ A method of propelling a boat with a pole
+ To place a bet, usually at long odds, or a risky one
As a noun it can be:
+ The former unit of money in Ireland
+ An open flat-bottomed boat (usually propelled with a pole)
+ The dent in the bottom of a wine bottle
Your usage matches that I've seen here before, but is not one with which I'm familiar. I wonder if it's preculiarly and specifically North American. In particular, though, it's the exact opposite of other meanings in other parts of the world.
So that's what they mean on "Dragon's Den" when they say "It's a punt for me.". I guess I assumed something similar, but was never really sure.