Is he a registered owner of any cars? If so, he could get insurance where he is at, whether it would be cheaper or not, is debateable. His age, type of vehicle, his address, driving record, all is taken into consideration. If he is under 25, full coverage,comp/collision, will be expensive. Young males pay higher rates, based on stats that they drive more recklessly, than the average driver. They are charging you for your son, because he is probably listed as a part-time driver on your policy. Having access to your cars, seems that rule is being pushed for all its worth, under your situation. Did they understand that he was in college, or did they think he was still a high school student? Their fees, and also your vehicle registration fees would be different, based on the location of the vehicle. Shop around, rates can vary quite a bit.

Where I am from (now this is RURAL New England), a young male driver principal operator with a NEW car away at school will be in the neighborhood of $3,000+ per year. Of course they will charge for him, he is PRINCIPAL operator of the vehicle. You would get a discount on your policy if he was over 100 miles away at school WITHOUT a vehicle. Him having the car THAT far away from you, the owner, you have NO control of what happens to it, who he lets drive it, etc, which is actually MORE of a risk than him being home with the car as a principal operator. Cars at school tend to have more accidents, more thefts, more damage in parking lots, etc. You are actually lucky your insurance company is letting you do this. Around here, that is grounds for nonrenewal of the policy, especially if the company is not licensed to do business in the state where it is kept most of the year (at the college). We have to get special permission to do this, then the company may charge the highest territory in the home state to get at least a little more premium for the higher risk the company is taking. It may or may not be less for him to get his own, first, he has to be the owner of the car (if it is new with a loan, you would have to refinance in his name), then the car will have to be registered in that state. If the state or area is more rural than where you are, call some agents for quotes, it can’t hurt. But if it isn’t, it is probably cheaper on your insurance since you have multicar credit & possibly account credit with your homeowners policy. Does he have a “B” or better average in school?? If so, he may qualify for Good Student credit which will help on the premiums.
Good luck to you. Can you raise your deductibles on that car? Or, can you send an older car to school with him? Maybe one that you can have liability only on?? That would help your premium immensely!