Sounds good. Fairly cheap to play, and easy to call a game at a moment's notice, although it'll be a bit heavy on your pockets for the rest of the day...
If you were playing this in a city, could you go into a bank and ask for five hundred pennies? Or would they just glare at you and ask you to leave?
And oh, looking at the scoring, it could be simpified to just "one point per coin", which would be a lot quicker to add up at the end.