Its December, in fact its mid-December – and lots of people have planned their great Christmas holiday, but have not booked anything. This is a critical error. Flight are expensive, hotel rooms are few, and booking a hire vehicle is going to be more difficult than you thought. My suggestion is that you make a plan, and make it quick. You have to decide whether your holiday is going to cost you more than you budgeted, or if you are going to drop the level of your holiday package.
With flights, there is not much you can do – little competition means that you will have to find the airline that has seats, and make the booking. My suggestion is that you make the biggest sacrifice in terms of accommodation. Instead of looking at the expensive hotels, search for a simple bed and breakfast, or get a double room in a backpackers. This would be your best option, and trust me, backpackers are often the best places to stay as you will meet the most amazing people. As for a car hire, you dont have to get that merc, go for a simple B group car with air-con and power-steering.
Dont make this difficult for yourself, book things immediately and online if possible. There are no more special deals going at this time, or if you do find a genuine one, grab it