Contact the seller and let him know your situation.
Be aware that many sellers have their invoicing accounts set to open an Unpaid Item Dispute automatically after 48-96 hours.
You should also be able to put the payment on your credit card, either by opening a Paypal account or possibly directly (which is actually through PP).
If you can do this it takes care of the entire problem, since the seller is paid instantly (unlike a payment from a bank account which is slowed down by the need for bank clearance).
And of course, you can then pay off your credit card at your leisure.
I don't have to tell you not to buy things you can't afford, since we are all grownups here.
