It seems slightly weak, but it is pretty novel. I wonder if you could get a coin token for every $1 you overpay without it being broken. Either that, or have it give 1 Coun token on play?
To match the standard wording of overpay, it would read "When you buy this, you may overpay for it. For each $2 you overpaid (rounding up), take a Coin token."