I was hit while at a red light, the estimate is for $3300, the car insurance wants to pay $1700, what can I do to recover the costs?

It depends on which insurance is offering to pay.  If you filed a claim against someone else's insurance, you can provide estimates, and appeal the amount you are offered. You can also file the claim against your own insurance and have your insurance company work to get the extra funds from the person that hit you.