Automobile shipping services can be expensive because it costs a lot of to operate a car carrier and transport a lot of cars to all destinations in the country. If you drove the car yourself you have to take into consideration the cost of gas (how many miles per gallon does it cost to drive your car) and you have to include lodging, meals, rest time, oil changes, tire replacement if necessary, and so on. These expenses are a lot more for an automobile hauler (this is what they get paid to do). Just think about the time and money this can save you not to mention the "wear and tear" on your car.
The winter shipping season is very different than the summer. Snow and bad weather in the northern states makes is hard for the drivers to run their routes. They have to be extra careful to make sure that your car arrives at its destination safely. There are a lot of people going to their "winter homes" for warmer weather, so there is more demand for these automobile haulers. Hence, taking that into consideration, prices can be higher. Southern routes in the US can be less expensive during those months since the wintertime can be their "slow season", thus lower prices for shipping.
Please keep in mind that you cannot ship a vehicle with personal items inside. This is due to the fact that auto transporters are licensed only to transport vehicles. Most will allow you to pack light items such as linens, towels and clothing as long is they are not visible from the windows and do not exceed 100 pounds. Nothing breakable can be put inside your car.