Auto Insurance Claims: Rental fees and devaulation, is it worth a suit

Question
I realize that I have the right to collect my rental fees from the at fault party in a car accident. They other person's insurance has already paid for the repairs in full, but only paid a part of the rental bill to me. They are telling that they will not cover rentals over a certain amount per day but the vehicle was the only one available. Keep in the mind that the cost was still reasonable, it was not like I was renting a sports car of luxury vehicle. In addition, I opted for insurance and they are refusing to pay that portion of the invoice as well. As it turns out, the difference is a significant amount ($1,000) for a 28 day rental, which is what happens since they took so long on the supplemental approval, not to mention they took 6 months to pay me. Do they have the right to determine rental costs and that I was not allowed to take the insurance?

Answer
I'm sorry for the delayed response, this one slipped through the cracks.

The laws are different in different states, so it is hard to answer this question.  This answer is a general answer that works in most cases and states. . .

1.  They do not owe you for insurance.  You were not required to purchase that, and in fact, you own auto insurance normally covers you and the rental car when you rent one as a temporary substitute for your insured vehicle.  

2.  The cost per day is something that is always argued.  I am not aware of any specific law in any State that regulates the rate of rental cars as it pertains to accident claims and reimbursement.

3.  You hit the nail on the head with the term "reasonable".  This is the standard that most courts use when evaluating how much one is owed for loss of use / rental.  If you can show that the costs you incurred were reasonable, and that they were the direct result of the negligence of the insurance company's policy holder, then you would likely be able to recover the costs if you sued.  The insurance company knows it is not likely worth it for you to sue them over $1000.00.  


Finally, let me say that I would sue the other party if the insurance company refused to be reasonable, even if the suit was over $1.  I am driven by principle, not economics.