It depends where you live. In East Anglia, it is very easy to get hold of - you just ask your local farmer. Anywhere else it is almost impossible without a big haulage fee.
I am about 3 miles from a big sugar beet factory, so can get pulp, nuts etc for next to nothing. I almost went to work for British Sugar, but got a better offer. The process/plant is amazing though.
In the winter I feed a bucketful of raw sugarbeet a day, as well as hay. The horses love them, and contrary to popular belief, it does not make them insane or crazy (despite the high sugar).