Long-distance moves can be a lot more complex, so your experience with cross country movers will likely differ from any time that you may have worked with local moving companies.
In general, you can expect to be charged based on the total weight of all of the items you are moving in the moving truck, the total mileage of your move, and the number of special services you choose from your moving company (such as if you need loading services or packing services).
You can simplify your move by using specialized services, but keep in mind that it will most likely drive your final price up quite a bit compared to handling the packing and loading of your belongings by yourself.